The Sign of the Four (SoundCraft Audiobooks) recap

Mary Morstan brings Sherlock Holmes a puzzle: her father vanished in London ten years ago, a stranger has sent her a valuable pearl every year since, and now that stranger wants to meet her. He proves to be Thaddeus Sholto, whose father served in India with Captain Morstan and came home with a stolen Indian treasure, concealing Morstan's sudden death during a quarrel over it. Thaddeus takes the party to his brother Bartholomew, who has just found the treasure hidden in the roof of the family house, and Bartholomew is found dead in a locked room, killed by a poisoned dart, with the treasure gone and a note signed the sign of the four. Holmes traces a wooden-legged convict, Jonathan Small, and his small Andaman Islander companion Tonga to a hired steam launch, and runs them down in a chase along the Thames. Tonga is shot and drowned, Small is captured, and the treasure has already been scattered into the river. Small confesses the whole history of the jewels and the betrayal behind them. Watson, freed of the barrier of Mary's inheritance, proposes to her and is accepted.

At Baker Street, Watson watches with disapproval as Sherlock Holmes, bored between cases, injects himself with a cocaine solution, and the two argue about it. Holmes demonstrates his methods on Watson's own pocket watch, reading from its scratches and pawnbroker's marks the history of the brother who owned it before him, which unsettles Watson considerably. A visitor is announced: Miss Mary Morstan, a governess, who lays out a strange series of facts. Her mother is long dead and her father, Captain Arthur Morstan of an Indian regiment, came home on leave in 1878, telegraphed her to meet him at his London hotel, and disappeared the same evening leaving all his luggage behind. His only friend in England, a Major Sholto of the same regiment, denied knowing that Morstan had returned. Six years ago an anonymous sender began posting her one very large pearl each year, and now a letter has come calling her a wronged woman and asking her to be at a theatre that evening with two friends but no police. She has also brought a paper found in her father's desk: a rough plan of a building, with a note beneath it signed by four men, one an Englishman named Jonathan Small and three with Indian names. Holmes takes the case, and he and Watson go with her.

Holmes finds that Major Sholto died in 1882, a few days before the first pearl was posted, which suggests the sender acted on something learned at his death. At the theatre the party is met by a coachman and driven a long way through the fog to a shabby house in a poor suburb, where the inside proves to be luxuriously furnished. Their host is Thaddeus Sholto, the Major's son, a nervous, hypochondriac little man who has been sending the pearls. He explains what his father confessed as he was dying. Sholto and Captain Morstan had come home from India in possession of a great treasure taken there. Morstan called on Sholto to claim his share, they quarrelled, and Morstan fell dead of a heart attack; Sholto concealed the body rather than face the suspicion, and kept the whole treasure, which is why he lived in fear and never told his sons where it was hidden. He was about to name the place when a face appeared at the window and the shock killed him. The brothers afterwards found the room ransacked and a note left on the body reading the sign of the four. Thaddeus has sent Miss Morstan the pearls out of conscience, and now reports that his twin brother Bartholomew has at last located the treasure in a sealed loft at the family house. They set off for Norwood to demand her share.

At Pondicherry Lodge the party is admitted by a prizefighting porter and finds the household in alarm. Bartholomew Sholto is dead in his laboratory at the top of the house, the door locked from within, his face fixed in a horrible grin. The treasure chest is gone and a note reading the sign of the four lies on the table. Holmes finds a poisoned thorn in the dead man's scalp, a hole cut in the roof above, a bare footprint far too small for a grown man, and marks left by a man with a wooden leg who climbed in from outside and left a trail of creosote after stepping in a spilled tin. He concludes that two intruders came from the roof, that one of them was carried up by a rope, and that they left with the chest by boat. Inspector Athelney Jones of Scotland Yard arrives, dismisses Holmes's reasoning, and arrests Thaddeus Sholto and the servants on the theory of a family quarrel over the money. Holmes ignores him and sends Watson across London to borrow a tracking dog, Toby.

Toby follows the creosote scent through south London, at one point leading them triumphantly to a barrel of the same chemical in a timber yard before being put back on the true trail. It ends at a wharf on the Thames belonging to Mordecai Smith, a launch owner who has been away from home since that night with his boat, the Aurora. Smith's wife recalls a wooden-legged customer who came for the launch in the small hours. The steam launch has therefore carried the fugitives and the treasure somewhere along the river, and Holmes cannot use the police to search for it without alerting them. Instead he calls in Wiggins and his crowd of street children and sets them to comb the whole riverside, wharf by wharf, for the Aurora, with a reward for the boy who finds her.

Days pass with no news. Holmes grows irritable and inactive while Watson visits Mary Morstan; Athelney Jones, whose case against Thaddeus Sholto has collapsed, comes to Baker Street in a much humbler frame of mind. Holmes eventually goes out disguised as an old sailor and discovers what the boys could not: the Aurora is hidden in a repair yard, being refitted with a new rudder, and is due out that evening. He arranges for a fast police launch and for Jones to come with them, and posts Watson and Jones aboard to wait. When the Aurora slips out, the chase runs for miles down the Thames past the docks, the police boat slowly gaining. On the deck beside the wooden-legged steersman crouches a very small dark figure who raises a blowpipe and fires a dart that passes between Holmes and Watson; both men shoot, and the small figure falls into the water and is not seen again. The launch is driven ashore on the mud flats, and the wooden-legged man, Jonathan Small, is dragged out and secured. The iron treasure chest is aboard, and Watson is given the task of carrying it to Miss Morstan.

Watson takes the chest to Mary Morstan and they force it open together: it is completely empty. Small threw the Agra jewels into the Thames one by one during the chase rather than let anyone else have them. Because the fortune that would have put her out of his reach is gone, Watson tells her that he loves her, and she accepts him. Back at Baker Street, Small tells his story. A young soldier in India, he lost a leg to a crocodile, and during the Mutiny he was on guard at the fort at Agra with three Sikh soldiers when a merchant's servant tried to smuggle a great treasure in; the four of them killed him and hid the jewels. They were convicted of the murder and sent as convicts to the Andaman Islands, where Small offered Major Sholto and Captain Morstan the secret of the hiding place in return for their freedom. Sholto took the treasure and broke the bargain. Small escaped years later with the help of Tonga, an islander whose life he had saved, hunted Sholto down and arrived too late to confront him, and came back for the treasure at last. He maintains that he never meant Bartholomew Sholto to be harmed and that Tonga killed him with the dart before he could stop it. Small is taken off to face the courts, Athelney Jones takes the official credit for the capture, Watson announces his engagement, and Holmes, with nothing left to interest him, turns back to his cocaine bottle.

The iron box recovered from the river is opened at Baker Street and found to be empty: during the chase Jonathan Small threw the Agra jewels overboard, a handful at a time, along miles of the Thames, so that no one should have what he was not allowed to keep. Watson takes the news to Mary Morstan, and because the fortune that would have separated them is gone he tells her he loves her; she accepts him, and the engagement is settled. Small then gives his full account. He lost a leg to a crocodile in India, served as a guard at Agra during the Mutiny, and with three Sikh soldiers killed a merchant's messenger for the jewels he was carrying, hiding them in the fort. The four were convicted of the murder and sent as convicts to the Andaman Islands, where Small bought his way toward freedom by telling Major Sholto and Captain Morstan where the treasure lay, on terms Sholto broke by taking the whole of it to England. Small escaped years later with Tonga's help, tracked Sholto down too late to confront him, and came for the treasure at last. He insists he did not want Bartholomew Sholto killed and struck Tonga for doing it. Small is taken away to face the charges, Athelney Jones receives the official credit, Watson has a wife, and Holmes, with nothing left to occupy him, reaches for the cocaine bottle.