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Baker Street Wiki

"Possibility Two" is the seventeenth episode of season one of Elementary. It first aired on CBS on 21 February, 2013.


While helping Joan learn deductive skills, Sherlock is approached by Gerald Lydon, a wealthy man suffering from an incurable disease that is destroying his mind. Even though the disease is genetic, Lydon is certain that someone gave it to him as part of a corporate power play. Sherlock is unconvinced and refuses the case. After Lydon kills his driver, however, Sherlock finds himself intrigued enough to take the case. Sherlock begins to believe Lydon when a scientist at a corporate genetics laboratory tells him that it is theoretically possible to induce the disease in another person, but the trail runs cold when she turns up dead. All the evidence, including DNA results, point to the killer being an ex-con unrelated to Sherlock's case. But can it really be that simple? Meanwhile, Sherlock sends Joan on an errand to a suspicious dry cleaning establishment in order to test her ability to solve a case without his help.


Part One[]

Marcus Bell shows Sherlock Holmes and Joan Watson the scene of a recent shooting: two men in security guard uniforms are lying next to each other in a parking lot. Watson, in her new role as Holmes's apprentice, attempts to reconstruct the scene and guess the likely direction the shooter took. Holmes steps in and points out the flaw in her deductions: the second "security guard"'s uniform is actually a hastily-assembled fake, meaning he is one of the two criminals involved, and was shot by the real security guard after being discovered. Holmes then tells Bell where to look for the accomplice who is still at large.

As they descend the stairs of the parking garage, Holmes tells Watson not to be discouraged; her initial observations were good, she just needs to learn to carry each one through to its logical conclusion. More than that, she needs to learn to recognize that which is out of place in seemingly mundane settings. As they emerge onto the street, Watson stops in her tracks and says she has just noticed something very out of place: a stretch limousine parked on the curb, whose driver is staring straight at them. The driver, Crabtree, introduces himself and says his employer, Gerald Lydon, would like a few minutes of their time. Holmes and Watson climb into the limousine.

Mr. Lydon is a renowned scientist, inventor, and philanthropist. He regrets to inform them that he has been diagnosed with dementia, and requires a full-time psychiatric nurse (who is riding in the limo with them), as a result of cerebral amyloid angiopathy (CAA), an incurable degeneration of the nervous system. The odd thing is, CAA is genetic, but there is no history of the disease in Lydon's family. Lydon is convinced that someone has given him the disease. He has already consulted geneticists (whose names he cannot remember at the moment), who tell him that it is possible to induce a genetic disorder. Holmes points out that "possible" and "likely" are not the same thing, and gently wonders if it is more likely that Lydon's dementia has caused him to become paranoid and delusional. Lydon says this is what his own family, and the police, believe, which is why he has no one else to turn to. He says Holmes has a reputation for being the best, and Lydon will pay any price for Holmes to find out who did this to him. Holmes regretfully says that he only takes cases where he honestly believes he is acting in good faith, and could not do so here, where the most likely explanation is that Lydon is suffering from a natural disorder. He asks Crabtree to pull over, then excuses himself and Watson, expressing his sincere condolences to Lydon.

That evening, Watson emerges from the bathroom and sees that Holmes has (again) piled a series of heavy books in front of her bedroom door. She comes downstairs while he is pouring acid onto a girl's doll, asking what Benthamite philosophy has to do with criminology or detection techniques. Before he can answer, the doorbell rings. Holmes answers the door to Crabtree, who is holding a small, octagonal wooden box. Holmes starts to refuse, but is briefly enthralled by the box's contents: a lone Osmia avosetta, a nearly-extinct species of solitary bee, famed for the beauty of the nests it builds. With difficulty, Holmes says he can't accept the bee, and asks that Mr. Lydon stop contacting him. Crabtree smiles graciously, and says he had already pegged Holmes as a man of conviction. Holmes cannot resist craning to take one last look at the bee as Crabtree turns away.

The next morning, Watson is practicing her single-stick moves under Holmes's eye, complaining that Holmes's hobby has nothing to do with learning how to be a detective. They are interrupted by a phone call from Captain Gregson, who informs them that Gerald Lydon has been arrested for shooting Crabtree, and is refusing to talk to anyone but Holmes.

Part Two[]

Holmes speaks with a shaken Lydon in his bedroom, while the police examine the scene of Crabtree's murder downstairs. Lydon knows what he has done, yet he cannot believe he has done it, much less articulate a reason why. He admits that with the onset of his dementia, he feels his hold on reality slipping away more and more, yet one thing he knows with absolute certainty is that his disorder is no natural occurrence, and someone has done this to him. "Help me!" he pleads.

Holmes comes downstairs, carrying the bee in the box. He informs Watson that they have taken Lydon's case. "I couldn't say no to him; it would have felt like denying a dying man his last wish." Having accepted Lydon's "bribe" (the bee), Holmes says they will stash it at home, then go to the genetics lab that confirmed Lydon's diagnosis.

At the company, Watt Helix, Holmes and Watson meet the company president, Ralph Keating and the head of their medical research division, Dr. Natasha Kademan. Dr. Kademan is surprised and pleased when Holmes recognizes her name, from her "sterling" dissertation, The Warrior Gene, in which she claimed to have discovered the gene responsible for sociopathic behavior. Unfortunately, her funding dried up, which is why she is now working in the private sector. Holmes discusses Gerald Lydon's suspicions with the two, and Kademan is non-committal. She says that, although it is theoretically possible to induce a genetic disorder, such a task would require a top-tier laboratory and a very large amount of money, not to mention that there are perhaps seven geneticists in the world brilliant enough to do it. Holmes, unfazed, asks for their names and addresses.

That evening, Holmes is perusing online profiles of the geneticists, and Watson comes downstairs, irritably waving a dry cleaning bill that Holmes taped to her door. He says he thought they were establishing a set of rules for living together; if she picks up his dry cleaning, he will commit to cleaning the refrigerator. Putting the bill aside, she asks about their investigation, and Holmes says he has something new to report: one of the seven most brilliant geneticists in the world (according to Kademan), resides in Norway, and just signed a home loan for some retirement property in a very exclusive quarter of Oslo (what used to be a royal garden, in fact). The man may be a brilliant scientist, but he is not wealthy, and the land is far outside what he can afford - which is why the loan was co-signed by Gerald Lydon's son, Carter. Holmes says he has booked them tickets to Oslo to interview the man in person - when suddenly his phone beeps with a text message from a blocked number. The caller sends a diagram of a molecule, and says it is not only possible to induce CAA in another person, but someone has actually invented the formula for doing so. Recognizing a phrase from the anonymous caller's message, Holmes looks through his copy of The Warrior Gene, and texts the person back to say he knows she is Natasha Kademan. He texts her to say that if she is concealing her name because she is afraid for her safety, they can protect her. She texts back to tell them to meet her at Watt Helix that night.

But when Holmes and Watson arrive, they find Kademan lying in the main lobby, stabbed to death.

Part Three[]

Examining the scene, Detective Bell is inclined to classify it as a burglary gone wrong, an idea which Holmes squelches quickly - "What were they here to burgle, blood samples?" He says it is far more likely that she made someone very nervous, likely the same someone who figured out how to poison Gerald Lydon. If it was a burglary, Holmes adds, why didn't the thieves take the most valuable object in the room, the portrait of the company's founder, Brian Watt - at least, it was the most valuable object before it's lower half was splattered with several droplets of the killer's blood. Taken aback, Gregson and Bell ask how he can be sure the blood is the killer's, when Kademan's is splattered all over the scene. Instead of replying, Holmes turns the question over to Watson. Though startled, she looks carefully and thinks for a few moments, then explains that Kademan was stabbed from the front, and the position of her body indicates she was facing away from the painting when it happened; on the other hand, the splatters on the painting are consistent with a defensive wound inflicted on her attacker.

They are interrupted when Paul Reeves, Kademan's distraught fiancé, rushes into the room and sees her body. When interviewed, Reeves, who is also a geneticist, says he knows Kademan was working with Gerald Lydon, but she never mentioned any suspicions that his CAA was deliberately induced, so he can't say who might have targeted her for that reason. In fact, Reeves says he is surprised that they haven't asked him about Benny Cordero, an ex-convict who participated in her Warrior Gene research, and appeared at Watt Helix the previous week to threaten her. Bell promises they will check him out.

Holmes denounces the Benny Cordero lead as a dead-end. Instead, he shuts himself up at the Brownstone with a molecular construction kit that takes Watson back to her Organic Chemistry days. Holmes is trying to recreate the diagram that Kademan texted to them the night before. By the next morning, Holmes has fallen asleep, and Watson, thanks to some help from her old genetics professor (whom Holmes swiftly deduces she had an affair with), has completed the molecule, which the professor called a work of genius. The molecule is a mutagen, designed to attack the specific gene in the human body responsible for CAA. Now, all they have to do is figure out who hired a genius to design it. Holmes says he greatly looks forward to that, but not before Watson retrieves his sweaters from the dry cleaner, as it is a freezing cold morning.

Watson is surprised by her experience at the dry cleaners: the staff consist of a laconic woman and a younger man in sunglasses, who speak almost no English and are positively surly when Watson presents the ticket. The woman quotes an outrageous fee, which the man hurriedly corrects, before Watson pays and takes Holmes's sweaters.

She meets up with him at the precinct, where he is watching Gregson and Bell interrogate Benny Cordero. Holmes impatiently says that Cordero is undoubtedly a sociopath, with prior convictions for blackmail and assault with a knife, but he is far too "prosaic" to be responsible for the crime they are investigating.

In the interrogation room, Cordero admits that he threatened Natasha Kademan - he volunteered for her research to make a favorable impression on the warden, but her study ended up calling him "an incurable sociopath", which doubtless extended his prison term - but swears that he didn't kill her, although he has no alibi for the night of the murder. Gregson and Bell are interrupted by impatient texts from Holmes, telling them Cordero is innocent. They try to ignore these texts, and Holmes resorts to pounding on the two-way glass and yelling through it, causing both policemen to storm out. Holmes tries to explain, and Gregson bitingly tells Holmes that, for the moment, Cordero's motive is much more plausible than some unknown person who believed she was going to expose a plot to poison Gerald Lydon with an incurable disease. Bell says they will check Cordero's DNA against the sample at the crime scene, and Holmes confidently predicts it will not match.

In a meeting with Lydon's younger son, Josh, Holmes asks that he be allowed to continue investigating. Carter Lydon comes in and says his father has just been declared legally incompetent, which means Carter speaks for the family and the company now, and he is firing Holmes and Watson immediately. Watson, thinking quickly, says their agreement with Gerald Lydon requires termination in writing, something he may no longer be capable of. Unimpressed, Carter writes "GET OUT!" on a notepad and passes it to her.

Leaving the office, Watson triumphantly waves the note in Carter's handwriting; Holmes nonchalantly says her instincts are good, but she needs to keep thinking ahead, and produces the pencil Carter used, along with an evidence bag for holding it. Since Josh was gnawing on the end of the pencil, it carries salivary DNA, which Holmes predicts will match Josh or his brother with the blood at Watt Helix.

Holmes calls Bell with the new lead, only to be caught off guard when Bell informs him that the blood at the crime scene was a perfect match for Benny Cordero.

Part Four[]

Shaken, Cordero swears that there must be some mistake, or else someone planted his blood at the crime scene. Gregson and Bell tell him the evidence is ironclad, and they are not interested in anything he has to say. They start to leave the interrogation room, and Cordero admits he has an alibi: he was at home, taking blackmail photos of his neighbor and the family's babysitter. Gregson and Bell are not sure what to think.

At the Brownstone, Watson is confused to find the same three sweaters that she picked up the day before outside her door, with another dry-cleaning ticket. Holmes, contemplating his evidence wall, apologetically explains that he spilled something on them, and they need to be cleaned again. Turning to the wall, he explains his dilemma: he still believes Benny Cordero is innocent, but the only explanation he offered - that someone planted his blood at the crime scene - while perfectly possible, is an "investigative dead end," and there is no way of proving or disproving it, since there is no evidence that anyone else was at Watt Helix - "Which is why I am considering Possibility Two." Watson notes that the section of the wall labeled "Possibility Two" is blank, and Holmes admits that he doesn't know what it might be yet.

When Watson returns after her second visit to the dry cleaner, she excitedly says she has figured it out: the dry cleaners are a front for some kind of illegal activity, since they do virtually no business and know nothing about dry cleaning - Holmes is testing her. Holmes tells her not to let her imagination run away with itself. He then introduces her to his panel of experts: six of the seven most brilliant geneticists on the planet, linked by a videoconference on his televisions. Holmes bids them goodbye, then turns to Watson and says that, after a lively discussion with the experts, he has discovered Possibility Two.

Police forensics labs rely on a standard DNA test called STR testing, which compares 13 genetic loci in two samples. This is actually a bit imprecise, since a human genome contains far, far more than 13 loci. All of Holmes's experts agree that technology has advanced to the point where it is possible to manufacture a fake DNA sample of 13 loci, even if the rest of the genome is too complex. Watson is disbelieving, and Holmes says he has proof that not only is such a thing possible, but it is exactly what happened here. Holmes obtained a sample of the blood from Watt Helix, and a colleague at Columbia subjected it to a full workup: the sample had 13 loci, which perfectly matched Benny Cordero's, but had no other loci at all. Someone took a blood sample, stripped it of its original genetic markers, and added a match for Cordero's. Watson remarks that almost everyone connected to their case is a geneticist. Holmes smiles and says true, but only one of those geneticists pointed them towards Benny Cordero in the first place...

Paul Reeves is brought in for questioning. He says it sounds far-fetched that someone could fake a DNA sample, but Gregson and Bell inform him that the police lab has already confirmed Holmes's findings, and point out that Reeves's employer, Ubient Phamaceuticals, has one of the best-equipped genetics labs in the city. Ordinarily, a search warrant would be required to examine the lab's equipment, but the company, eager to be helpful, has already thrown its doors wide open. Gregson and Bell vow that if Reeves used their equipment to make the phony blood, they will find evidence of it, and invite him to confess before that happens.

Ruefully, Reeves admits that he killed Natasha. When they first got engaged, they did genetic workups on each other, and it turned out that Reeves has the "warrior gene" that, according to Kademan's thesis, makes him a sociopath. She assured him that it wouldn't change their relationship, but he says he could feel her growing more distant from him - spending more late nights at Watt Helix, canceling dates over and over again. He also knows for a fact that she had taken up with another man, whom he identified as Lincoln Dunwoody. Reeves admits that he made the fake blood a while ago, anticipating that their relationship was about to end, but the final straw came on the night she died, when she canceled a dinner date on his birthday to stay at the lab.

Holmes asks what any of this has to do with someone's plot to induce CAA in Gerald Lydon. Reeves appears genuinely baffled - he is admitting, on the record, that he killed Natasha, but he has no idea whether it is even possible to induce CAA, and has no idea what Holmes is talking about.

After Reeves is arrested, Watson finds Holmes in an unused closet of the precinct, examining multiple post-it notes with the name "Lincoln Dunwoody" written on them. She says the case is closed, and they have caught Natasha Kademan's murderer. Holmes insists that there is still a "Possibility Two" to be explored - the name "Lincoln Dunwoody" is so unusual that it has to mean something more bizarre than the name of Natasha's suspected lover. Furthermore, Holmes can find no record that any such person exists.

Holmes eventually finds the thread: "Lincoln" and "Dunwoody" are both the names of charitable foundations prominent in New York, whose founders have, sadly, just been institutionalized for dementia.

Holmes and Watson go to visit Greta Dunwoody, matriarch of the Dunwoody family, in a private hospital. A few minutes' conversation is enough to show that her dementia is no act: at first she mistakes them for her own children and, after thanking them for the flowers they brought, asks them to give her some privacy so she can continue practicing her piano for her upcoming audition at Julliard (apparently under the belief that she is a teenaged girl and aspiring art student). Whatever was done to Gerald Lydon has also been done to at least two of New York's wealthiest.

Part Five[]

Watson enters the kitchen of the Brownstone and sees Holmes cleaning the refrigerator. She is surprised, since he said he wouldn't be doing that until the case was solved. Holmes breezily tells her that it is, but, rather than reveal the solution, he invites Watson to work it out for herself.

Watson thinks carefully: at first, their prime suspect was Carter Lydon, but he has no motive to poison anyone other than his father. His co-signing of the home loan for the geneticist in Norway was highly suspicious, but explicable if Carter was hiring that geneticist to find a cure for his father's condition, rather than to develop the poison that induced it.

The next question is, who has the motive to induce CAA in New York's wealthiest citizens? The first, best answer is, people who are researching the disease themselves. Since not everyone so afflicted would donate, or donate to the same cause, their unknown poisoner would have to target more than one person.

Holmes confirms that, after their founders were taken ill, the Lincoln and Dunwoody Foundations both gave generous grants to Watt Helix, well-known for its research program into CAA. Natasha Kademan must have discovered the conspiracy, hence the repeated references in her notes to "Lincoln" and "Dunwoody." This makes her death all the more tragic, since Reeves mistook her preoccupation with her work at Watt Helix as proof that she was cheating on him.

Watson says that their prime suspect must be the smartest scientist at Watt Helix, and starts to flip through a brochure for the company. Holmes closes it, and says the smartest scientist at Watt Helix no longer works there on a daily basis.

The company's founder, Dr. Brian Watt, is brought in for questioning with his attorney. He says almost nothing during the interview, but he doesn't need to: his medical records have already confirmed that he was diagnosed with the gene responsible for CAA early in his life. Holmes says Watt knows he is a "time bomb," and that he is desperate to find a cure before the onset of dementia. Holmes wonders aloud whether that was what motivated him to become a doctor in the first place. Gregson says they will be able to find proof of his work in Watt Helix's lab,and that he used its facilities to develop the poison.

At the dry-cleaning establishment, the man and woman are watching the news coverage of Watt's arrest, when Watson enters. Instead of a dry-cleaning ticket, she has brought Bell and a squad of uniformed cops, who have a warrant to search the premises for signs of illegal activity: money laundering, gunrunning, etc.

Watson returns to the Brownstone in triumph, and Holmes tells her to shut the door quickly; the Osmia avosetta has escaped its cage, and Holmes is desperately trying to recapture it before it flies away. Watson informs him that the "bust" of the dry cleaners was successful, and Holmes congratulates her on her quick thinking - "I thought I was going to have to send you back there three more times."

Watson asks why Holmes didn't tell her the truth earlier, when she began to suspect something. Holmes slams the jelly jar in his hand down on the bee, trapping it on the surface of a book, and explains that every good detective needs to learn at least two vital lessons: one, to trust his or her instincts; and two, that every encounter, no matter how seemingly routine, has the potential to lead to the most bizarre and labyrinthine crimes.



Guest stars[]

  • Dennis Boutsikaris – Gerald Lydon
  • Christopher Sieber – Carter Lydon
  • Michael Izquierdo – Josh Lydon
  • Steven Hauck – Crabtree
  • Bennett Bradley – Ms Tompkins
  • Jennifer Lim – Natasha Kademan
  • David Furr – Paul Reeves
  • Gibson Frazier – Raph Keating
  • Albert Jones – Benny Cordero
  • Barbara Miluski – Agnieszka
  • Aleksander Mici – Ludoslaw
  • Tom Galantich – Brian Watt
  • Caroline Strong – Ashley Mitchell
  • Annalaina Marks – Miss Angel
  • Patricia Conolly – Greta Dunwoody
  • George Bartenieff – Jurgi


  • Crabtree mentions that Holmes was recommended by a "Mr Musgrave" in London, a reference to the story "The Musgrave Ritual".
  • In Part One, Holmes mistakenly refers to the solitary bee as an "Omnia avosetta"; the correct term, which he uses in Part Five, is Osmia.

Season One navigation[]

Season One
#01 Pilot#09 You Do It To Yourself#17 Possibility Two
#02 While You Were Sleeping#10 The Leviathan#18 Déjà Vu All Over Again
#03 Child Predator#11 Dirty Laundry#19 Snow Angels
#04 The Rat Race#12 M.#20 Dead Man's Switch
#05 Lesser Evils#13 The Red Team#21 A Landmark Story
#06 Flight Risk#14 The Deductionist#22 Risk Management
#07 One Way to Get Off#15 A Giant Gun, Filled with Drugs#23 The Woman
#08 The Long Fuse#16 Details#24 Heroine