The film is divided into two separate, unequal stories. In the shorter of the two, Holmes is approached by a famous Russian ballerina, Madame Petrova (Tamara Toumanova), who proposes that they conceive a child together, one who she hopes will inherit her physique and his intellect. Holmes manages to extricate himself by claiming that Watson is his lover, much to the doctor's embarrassment.
Consulting detective Sherlock Holmes fakes his own death in Scotland in order to investigate a number of bizarre apparent suicides that he is convinced are part of an elaborate plot by "a female Moriarty". Returning to his assistant Watson in secret, Holmes notes that all the victims were wealthy gamblers, so disguised as "Rajni Singh", a distinguished Indian officer, he stalks London's gaming clubs.
Detective Morris Flynn (Hans Albers) and his assistant Macky McMacpherson (Heinz Rühmann), masquereading as Sherlock Holmes and Dr Watson, investigate two attractive sisters, Mary and Jane Berry, and the theft and forgery of valuable postage stamps.
Dr. Watson is serving as resident doctor at Musgrave Hall in Northumberland, a stately home which is also used as a hospital for a number of servicemen suffering from shell shock.
Several centuries later, the death of Sir Charles Baskerville is being reported by his best friend Dr. Richard Mortimer (Francis de Wolff) to Sherlock Holmes (Peter Cushing) and Dr. Watson (André Morell), who are willing to meet the new owner of Baskerville Hall, Sir Henry (Christopher Lee). After meeting Sir Henry, Holmes remembers that he is going to be away on another case when Sir Henry returns to Baskerville Hall. Holmes puts Watson in charge of watching over Sir Henry. A tarantula attacks Sir Henry briefly in London; Holmes suspects foul play. Before he leaves, Holmes reminds Watson not to let Sir Henry go out onto the moor after dark.
Sherlock Holmes is a fictional character created by Dr. John Watson (Ben Kingsley) as the central character in a series of short stories published in Strand Magazine. Watson uses the character to enable him to solve crimes incognito, so as not to disrupt his career as a doctor during a period when he was applying for a post at an exclusive hospital, one in which the senior staff would frown on Watson's "hobby". Although he does not secure the job, Watson decides to satisfy public demand to see Holmes in person by hiring unemployed actor Reginald Kincaid (Michael Caine) to play the part of the fictional detective.
Justin Playfair (Scott) is a millionaire who retreats into fantasy after his wife's death, imagining himself to be Sherlock Holmes, the legendary fictional detective. Complete with deerstalker hat, pipe and violin, he spends his days in a homemade criminal laboratory, constantly paranoid about plots hatched by his (Holmes's) archenemy, Professor Moriarty.
Teenagers Sherlock Holmes (Nicholas Rowe) and John Watson (Alan Cox) meet and become good friends as students at London's less-than-prestigious Brompton Academy. Watson is introduced to Holmes’ mentor, Rupert T. Waxflatter (Nigel Stock), a retired schoolmaster and inventor. Waxflatter's niece Elizabeth Hardy (Sophie Ward) is also Holmes’ close friend and love interest. Holmes is generally recognized as brilliant but considered an undisciplined troublemaker by most of the school administration. He is closest to Professor Rathe (Anthony Higgins), his fencing instructor, who warns Holmes that he is too emotional and impulsive.
A convicted thief in Dartmoor prison (played by an uncredited Cyril Delevanti) hides the location of stolen Bank of England printing plates inside three music boxes (each of which plays a subtly different version of "The Swagman"). The boxes are sold at a local auction house.
In 1947, the long-retired Sherlock Holmes, aged 93, lives in a remote Sussex farmhouse with his housekeeper, Mrs Munro, and her young son Roger. Having just returned from a trip to Hiroshima, he starts to use jelly made from the prickly ash plant he acquired there in an effort to improve his failing memory. Unhappy about his ex-partner Watson's fictionalisation of the story of Holmes's last case, the fictitious “The Adventure of the Dove Grey Glove”, he hopes to write his own account but is having trouble recalling the details. As Holmes spends time with Roger, showing him how to take care of the bees in the farmhouse's apiary, he comes to appreciate Roger's curiosity and intelligence and develops a paternal liking for him.
Sherlock Holmes et le docteur Watson sont sur la piste de Jack l'Éventreur. Leur enquête va les mener dans l'entourage de la famille royale, du gouvernement britannique et de la franc-maçonnerie.
A British agent carrying a vital document is murdered on his way to deliver it in the USA. Holmes deduces he was carrying the document in the form of microfilm and goes to Washington with Watson to find the killer and retrieve the document before it falls into the hands of an "international spy ring". Before his death, the agent managed to pass the microfilm into the unwitting hands of a Washington debutante and bride-to-be. There are some amusing moments when the microfilm, which has been inserted into a "V for Victory" matchbook, gets passed from hand to hand at a party unknowingly, and at one point is discarded by the chief criminal. Holmes and Watson track down the criminals, rescue the bride-to-be and regain the microfilm.
About to leave London for a much-needed vacation, Holmes and Watson receive a cryptic invitation. Intrigued, Holmes accepts and is met by the prime minister of the fictional country of Rovinia, who begs him to escort Prince Nikolas home. It turns out that his father has been assassinated, and Nikolas is the heir. Holmes agrees.