Sherlock Holmes is engaged by Miss Mary Morstan, who has received annual pearls and a mysterious summons linked to her father’s 1878 disappearance.
His inquiry uncovers the Agra treasure misappropriated by Major Sholto, the murder of Bartholomew Sholto, and forensic evidence implicating Jonathan Small, a wooden‑legged ex‑convict, and his Andaman accomplice Tonga.
Holmes intercepts the thieves at sea—Tonga is killed, Small captured and admits scattering the loot in the Thames—and the case closes while Watson and Mary form a personal attachment.

Sherlock Holmes and Dr. Watson tackle a series of cases: a leaked scholarship paper, the golden pince‑nez murder with its Russian secret, the vanished three‑quarter that leads to a tragic domestic death, the Abbey Grange homicide revealed as an act of protection, and the disappearance of a diplomatic despatch that might have provoked war.
By minute observation, clever experiments and relentless questioning Holmes exposes lies, locates hidden evidence and discerns motives.
With discretion and stern compassion he averts scandal where he can, brings culprits to light or spares the innocent when justice and mercy permit.

Three short narratives: in "The Greek Interpreter" Mr. Melas, an interpreter, is terrorized into assisting two English villains who hold Paul Kratides captive to extort his sister’s fortune; Holmes and the police rescue Melas and the victims though the principal conspirators escape.
In "The Naval Treaty" Percy Phelps, a Foreign Office clerk, loses a secret naval document which Holmes proves was stolen and concealed by Joseph Harrison and then recovers, thereby averting political ruin.
In "The Final Problem" Holmes describes and pursues Professor Moriarty’s criminal network; after a European chase the two men confront one another at Reichenbach Falls and are lost, while Holmes leaves materials that dismantle the gang.

Dr. James Mortimer brings Sherlock Holmes the Baskerville legend and the strange, apparently fright‑induced death of Sir Charles; Holmes swiftly extracts key facts from physical evidence and agrees to advise about the heir, Sir Henry.
Dr. Watson, sent to Dartmoor to protect Sir Henry, reports local findings—the Barrymores secretly shelter an escaped convict, a threatening anonymous letter and missing boots, and the Stapletons are suspicious neighbours.
Holmes, operating covertly, proves that Stapleton (possessionally posing as a naturalist) engineered a luminous, chemically treated mastiff to terrorize heirs; the hound is killed, Selden is found dead, Stapleton perishes in the Grimpen Mire, and Holmes reconstructs the criminal plot.

An engineer hired to mend a hydraulic press is lured into a coining gang’s lair, narrowly escapes being crushed but loses his thumb, and the counterfeit works are later destroyed by fire.
Lord St. Simon’s bride vanishes at her wedding; Holmes shows she eloped with a long‑lost American lover rather than suffer a public scene.
Holmes then clears an accused son by exposing Sir George’s theft of three beryls and recovering them, and rescues Violet Hunter from the sinister household at the Copper Beeches where a girl had been secretly imprisoned.

Dr. John H. Watson, returned from Afghanistan, becomes the roommate and chronicler of Sherlock Holmes, a consulting detective who applies rigorous observation and analytical deduction.
Holmes unravels the linked murders of Enoch J. Drebber and Joseph Stangerson in London—using footprints, a found ring and toxicological tests he identifies the cabman Jefferson Hope as the perpetrator.
Part II supplies the motive: a Utah backstory in which Hope avenges the forced marriage and death of Lucy Ferrier and her father at the hands of Drebber and Stangerson; Hope confesses but dies of an aortic aneurism after capture.

Father Brown recounts how Prince Otto, hunting for hidden gold, was stealthily gagged with his own military sash at a hermitage; mute and fleeing, he was then killed by a palace sentry (Schwartz), whose rescuer Hedwig later married. Brown, calling the affair a grim fairy-tale, lingers on the suspected double treachery of the Chamberlain.

Former criminal Flambeau, now retired in Spain, receives Father Brown and a series of visitors whose intrigues yield several puzzling murders and thefts.
Father Brown’s method—moral-intuitive immersion in a suspect’s mind to reconstruct motive and opportunity—resolves each case and frames a wider argument about remorse, repentance and the limits of scientific criminology.
The volume closes with Flambeau’s frank confession of his past and a sustained plea for humane understanding and forgiveness.

1) After Pauline Stacey's fall, Father Brown proves the sun‑prophet Kalon murdered her by exploiting her hereditary blindness, while Joan Stacey's manipulation of the will supplied a secondary motive.
2) Investigating Sir Arthur St. Clare's legend, Brown reconstructs that St. Clare killed Major Murray to hide corruption, fomented a needless slaughter to bury the crime, and was later executed by his own men while history sanctified him.
3) In Sir Aaron Armstrong's death Brown shows it was a suicidal episode misread as murder: a chaotic rescue involving shots, a rope and a knife accidentally precipitated the fatal fall, exonerating Patrick Royce.

Hercule Poirot is called to the Villa Geneviève where Paul Renauld is found stabbed and buried in an apparently staged, bewildering crime involving a love-letter from “Bella,” a stolen aeroplane dagger and a second corpse.
By methodical deduction Poirot exposes a convoluted scheme—Renauld (formerly Georges Conneau) had planned to fake his death using a dead tramp, but Marthe Daubreuil, scheming to secure the fortune and Jack’s hand, actually killed him; Bella (Cinderella/Dulcie) stole the dagger to protect her sister and later confessed to save Jack, who is ultimately cleared.
The case ends with Marthe dead, Bella spared and loved by Hastings, Jack reconciled with his mother and departing for South America, and Poirot triumphant.

Hastings returns to England and, with Poirot, uncovers a shadowy international cabal—the "Big Four"—whose mastermind is the Chinaman Li Chang Yen.
A string of murders, abductions and audacious disguises point to an American financier, a brilliant French scientist and a protean English "Destroyer" who strike worldwide.
Poirot feigns death, lures them to their Dolomite stronghold and, in a final confrontation, exposes and overthrows the conspiracy.

Poirot reveals that the murder of Madame Kettering was a premeditated plot by Richard Knighton (alias the Marquis) and his accomplice Ada Mason: they killed her on the train, disguised and planted the body to create an alibi, stole the rubies and arranged their delivery to Papopolous.
Knighton's assumed identity and feigned limp are exposed, Derek Kettering is released, Van Aldin expresses gratitude, and Poirot later consoles Lenox while reflecting on Katherine's reticence and the metaphor of life as a train.

Violet Marsh asks Poirot to locate a second will after her rich uncle’s testament gives her only a year at Crabtree Manor to “prove her wits.” Poirot’s inquiry—interviews, a hidden fireplace cavity and a burned fragment—leads him to the desk key’s envelope, whose invisible-ink writing is revealed by heat. The revealed document, dated later, bequeaths the estate to Violet, so her appeal to an expert secures her inheritance.

Captain Hastings investigates the murder of Harrington Pace at Hunter’s Lodge after the Hon. Roger Havering summons Poirot; the scene yields a missing revolver and a vanished “housekeeper.” Poirot concludes Mrs. Havering, a former actress, disguised herself as the housekeeper to provide an alibi while her husband planted a false clue in Ealing, securing the uncle’s fortune. Lacking prosecutable evidence, they evade conviction but later die in an air‑crash.

Flossie Halliday (Mrs. Rupert Carrington) is found chloroformed, stabbed and robbed on the Plymouth Express; her father engages Poirot.
Poirot reconstructs the timing, the maid’s odd behaviour, a love-letter and pawnbroker leads and concludes the murder was staged so the maid could impersonate the victim while an accomplice fenced the jewels.
He exposes Jane Mason as Gracie Kidd by finding duplicate clothes and facilitates the arrest of Red Narky.

Series of short detective cases narrated by Captain Hastings, centred on Hercule Poirot.
Each story presents thefts, murders or frauds unraveled by Poirot’s methodical deductions, psychological insight and attention to small details.
Recurring motifs include imposture, staged incidents, insurance/inheritance schemes and the primacy of “method.”

Hastings records the sudden death by poisoning of Emily Inglethorp at Styles and recounts Hercule Poirot’s systematic inquiry into conflicting alibis, forged clues and a destroyed will. Poirot demonstrates that Alfred Inglethorp, assisted by Evelyn Howard, precipitated strychnine into the victim’s medicine and manufactured evidence to frame John Cavendish, and the hidden letter fragments provide the conclusive proof.