Plot - From Wikipedia Edit
John receives news of an explosion on Baker Street and rushes back home, only to find Sherlock safe and Mycroft pressing Sherlock to investigate the murder of an MI6 clerk and the disappearance of a flash drive with important defense plans. Sherlock refuses and is then called to Scotland Yard. Inside the bombed-out flat was a strongbox containing a mobile phone similar to the one belonging to the victim from "A Study in Pink".
A message leads Sherlock to a pair of trainers. He then receives a call from a terrified woman, reading a message from a third party. If Sherlock doesn't solve the puzzle in twelve hours, the explosive vest she is wearing will detonate. While Sherlock examines the trainers, Molly Hooper interrupts him and introduces her new boyfriend Jim. Sherlock deduces that Jim is gay, and Molly storms out. Sherlock traces the shoes to a schoolboy drowned in a pool in London. He proves the boy was poisoned with botulinum via his eczema medication. Sherlock announces the solution to the bomber. The woman hostage is freed.
A second message shows a blood-stained sports car, and another hostage phones Sherlock to give him eight hours to solve the mystery of its missing driver. Sherlock interviews the missing man's wife, then the owner of the car rental, and deduces that he was recently in Colombia. Finding the blood in the car had been frozen, Sherlock concludes the lost man paid the agency owner to help him disappear. Sherlock announces the solution. Once again, the hostage is freed.
A third message and hostage point Sherlock to the death of a television personality apparently from tetanus from a cut. However, the wound was made post-mortem. Sherlock pins the crime on the housekeeper, also her brother's lover, who murdered her by increasing her botox dose. Although Sherlock solves the puzzle, the blind hostage starts describing her kidnapper's voice. The kidnapper detonates the bomb, killing her and eleven others.
The fourth message is a photograph of the River Thames without hostage calls. At the matching riverbank, Sherlock finds a security guard's corpse, identifying it as the work of an assassin called Golem. Sherlock tracks him down, but is too late to stop another murder, an astronomy professor whom the guard talked to after he realised a recently discovered painting by Vermeer was a fake. While Sherlock is examining the painting, the fourth hostage, a child, calls and gives Sherlock ten seconds to prove the forgery. He spots a supernova within the painting that occurred centuries after the real painting was made, just in time to stop the bomb. The museum curator confesses the forgery and that her accomplice was called Moriarty.
Investigating Mycroft's case in secret, Sherlock and John trace the MI6 clerk's death to his prospective brother-in-law, who confesses he stole the flash drive and accidentally killed him. The man still has the drive since he had no idea how to sell it. Sherlock uses it to lure out Moriarty, but John shows up instead, wearing an explosive vest. Moriarty appears and turns out to be Molly's boyfriend, Jim. He tells Sherlock to stop interfering, but Sherlock refuses. Moriarty leaves momentarily, and Sherlock takes off John's vest. Moriarty soon returns with multiple snipers targeting both Sherlock and John. Sherlock aims his handgun at the explosive vest – mutual assured destruction.