Season synopsis
Contains spoilers for this season and earlier seasons.
John Watson returns from Afghanistan injured and struggling to settle into civilian life. A mutual acquaintance introduces him to Sherlock Holmes, who needs a flatmate at 221B Baker Street. John soon accompanies him to a death that Scotland Yard considers part of a series of suicides. Sherlock traces the killings to a taxi driver who makes victims choose between two apparently identical pills, one poisonous. John shoots the driver before Sherlock can take his chosen pill, but the dying man names Moriarty as his sponsor. Sherlock protects John from police suspicion, and their partnership takes shape.
Coded messages at a bank and a library lead them into the Black Lotus smuggling operation. Two couriers have been killed over a missing antique, and museum expert Soo Lin Yao dies after explaining her connection to the gang. When John and his date Sarah are kidnapped, Sherlock deciphers the messages using a London street guide and reaches them in time. The stolen treasure turns out to be a valuable jade hairpin given to a secretary who did not know its significance.
A bomber then forces Sherlock through timed investigations, making hostages relay the instructions while wearing explosives. The cases include a schoolboy’s poisoning and a forged painting whose impossible star proves it a fake. John investigates stolen missile plans, bringing the two enquiries together. At a swimming pool, Sherlock finally meets Jim Moriarty, who had previously posed as Molly Hooper’s boyfriend. John arrives strapped into an explosive vest. Sherlock removes it, but Moriarty returns with snipers covering them both. Sherlock points his gun at the discarded explosives, leaving all three caught in a deadly standoff.