René Heron was a revolutionary and the brother of Madame Simza Heron. He is portrayed by Laurentiu Possa. Though his dealings with the anarchist leader Claude Ravache, René came to work for the criminal mastermind Professor James Moriarty. Sherlock Holmes teamed up with his sister in order to find him and uncover Moriarty's plot.

Holmes eventually realised that Moriarty had been raising tensions throughout Europe so a peace conference would be called at the Reichenbach Falls in Switzerland. Moriarty would then have Heron murder either the German chancellor or the French prime minister. Holmes realised that in order to ensure a war, Moriarty had had Dr Karl Hoffmanstahl give Heron facial surgery to make him look like a known diplomat. With the real ambassador murdered and replaced with Heron, the assassination by an apparent government agent would definitely cause a war to break out. However, he was foiled when Dr John Watson worked out his identity as the ambassador of Rumania and tackled him to the ground, causing his shot to miss hitting the chancellor. Because of his failure, Moriarty had Colonel Sebastian Moran shoot him with a curare dart shortly after his arrest to silence him. Though Watson and Sim tried to revive him, he died in his sister's arms.