21. The Man with the Twisted Lip

Complete story — includes the ending

Sherlock and Joan investigate the disappearance of Paige, the sister of a woman who frequents Sherlock's sobriety meetings. At the brownstone, they are surprised by Mycroft, who returned to New York, apparently to focus on Diogenes. Later, Joan meets Sherlock at a park he found based on a clue in one of Paige's songs. The pair find two bodies there, Paige's and that of a Zach Piller, who manufactured drones for a company called McCarthy-Strauss. The two victims were killed by Piller's drones. Sherlock later visits Diogenes and sees Guillaume de Soto, a high-ranking member of French drug cartel Le Milieu. Sherlock then captures a drone that was spying on him. Piller's psychiatrist says that he accidentally misidentified ten undercover CIA agents in Afghanistan, who were then killed by friendly fire. He subsequently wrote a report on it out of guilt. The psychiatrist is eventually poisoned by another drone. To incriminate McCarthy-Strauss, Sherlock waits at a pier to meet with the business executive that Piller's report belongs to, while Joan breaks into the executive's office and steals the report. That night, Joan follows de Soto's contact Marchef outside Diogenes after he receives an envelope. She retrieves the envelope, but finds a picture of herself inside. The contact kidnaps her.