Mycroft and Scotland Yard detectives including Greg Lestrade bring Sherlock various cases, hoping they will reveal Moriarty's scheme.
Sherlock quickly solves the case, and reveals that the son was hiding in the car, planning to surprise his father, but died from a seizure.
Sherlock notes that a bust of Margaret Thatcher at Welsborough's home was missing from its place and finds that it had been stolen and smashed upon the front porch.
Six years prior, a rescue mission of hostages held at the British embassy in Tbilisi went wrong when the captors were tipped off and killed everyone on the team except Ajay and Mary.
He reveals that, while being tortured and held in Tbilisi, his captors kept taunting him with the word "Ammo" and told him he'd been betrayed by "the English woman", whom he assumed to be Mary.
John, Mycroft and the police arrive, and Vivian shoots at Sherlock, but Mary jumps in the way, taking the bullet.
[6] Joanna Robinson of Vanity Fair, notes that Holmes' request to be reminded of Norbury as an example of his over-confidence is a reference to "The Adventure of the Yellow Face".
The other reference to Doyle's "Adventure of The Yellow Face" is when John Watson says to Mary: "I might not be a very good man, but I am better than you give me credit for."
This sentence was spoken by Grant Munro to his wife Effie (who, like Mary Watson in "Sherlock", was also hiding a secret) in "The Adventure of The Yellow Face.
Toby, the dog Sherlock borrows to aid in his search for clues, is referenced in The Sign of the Four, where a trained scent hound helps track Holmes and Watson to a boat landing.
The "A.G.R.A" team mentioned in this episode alludes to the Agra Fortress in The Sign of the Four which the character Johnathan Small had to flee during the 1857 rebellion.
"[10] The Daily Telegraph gave a good review with a rating of 4/5 stars, calling it "a dizzying triumph of complex plotting.
"[11] After Ralph Jones, in an opinion piece in The Guardian, criticised the episode for making Sherlock into a James Bond-style action hero, Mark Gatiss wrote in personally and responded in the form of verse.