Madame Simza Heron, also known as Sim, was a Romani gypsy who assisted Sherlock Holmes and John Watson in their fight against Professor Professor Moriarty's plans to spark a European war.

She first meets Holmes in a London club where she is working as a fortune teller in the same club that Holmes and Watson are attending Watson's bachelor party. Holmes visits her and deduces that there is an assassin hiding in the ceiling waiting to kill her and fights him whilst Sim attempts to escape.