Sherlock Holmes is bored without stimulating cases.
Mycroft Holmes urges Sherlock to investigate the death of
Secret Intelligence Service clerk Andrew West and the disappearance of a
flash drive containing missile plans. Sherlock refuses and then is called to
Scotland Yard where
Lestrade hands him an envelope containing a
mobile phone identical to the victim's phone from "
A Study in Pink". The phone shows a photo of a derelict room, which Sherlock recognises as the unoccupied flat 221c, downstairs from 221b. Sherlock,
Watson and Lestrade enter the room and find a pair of
trainers in the middle of the floor. The mobile rings, and the caller – a frightened hostage reading texts from her captor – states that if Sherlock cannot solve the puzzle in twelve hours, a bomb will kill her. After closely examining the shoes, Sherlock realises they belonged to Carl Powers, a schoolboy who drowned in a swimming pool 20 years previously. Evidence on the laces indicates that
botulinum toxin was introduced into the boy's
eczema medication, leading to his paralysis. Sherlock announces the solution to the bomber, and the hostage is freed. A second message shows a blood-stained sports car, and another hostage phones, giving Sherlock eight hours to solve this mystery. Finding the vehicle without its driver, Sherlock interviews the missing man's wife and the manager of the agency where the car had been rented. After finding that the blood in the car had been frozen, Sherlock announces that the missing man paid the rental agency owner to
help him disappear, and the hostage is freed. A third message and hostage point Sherlock to the recent death of TV presenter Connie Prince, who allegedly died from
tetanus. Watson interviews Prince's brother Kenny, and Sherlock shows that housekeeper Raoul de Santos — Kenny's lover — murdered Connie by increasing the dosage of her
botox injection. Despite Sherlock solving the puzzle, the hostage is killed, along with several others, for describing the kidnapper's voice. The fourth message is a photograph of the
River Thames, but no hostage calls. Sherlock and the police discover security guard Alex Woodbridge's body on the riverbank. Sherlock claims that Woodbridge was strangled by an
assassin called the "Golem". He also deduces that Woodbridge worked at a local art gallery that is preparing to display an allegedly "lost"
Johannes Vermeer painting. Watson visits Woodbridge's flat and finds he was interested in astronomy but not art and that a recent message on his answering machine from a professor stated that he'd been right about something. Sherlock deduces that the Vermeer painting is a forgery and that Woodbridge's discovery of it was why he was killed. The hostage calls and Sherlock gives his answer, but the hostage, a child, begins counting down. Realizing he must prove his deduction, Sherlock spots a
supernova in the painting that actually appeared 200 years after Vermeer, thus saving the child. The museum curator confesses setting up the forgery and outs her accomplice: a man named "
Moriarty". At Mycroft's insistence, Watson investigates West's death, and he and Sherlock track down Joe Harrison, the brother of West's fiancée, who admits to stealing the flash drive and accidentally killing West when he was confonted. Unable to sell it, Harrison kept the drive and gives it to Sherlock. Realizing that West's death and the missing flash drive were the fifth mystery, Sherlock texts the bomber, offering to turn over the device. But at the meeting place, it is Watson who arrives as the fifth hostage, wearing an
explosive vest. Moriarty – who'd been seen earlier as
Molly's new boyfriend Jim – appears and introduces himself as "a specialist, just like you." After taunting and threatening Sherlock, Moriarty leaves but returns after Sherlock removes Watson's vest. With multiple snipers aiming at Sherlock and Watson. Sherlock aims his handgun at the explosive vest, threatening
mutual assured destruction. == Sources and allusions ==