In 1891, London detective Sherlock Holmes (Robert Downey, Jr.) and his partner and flatmate Dr. John Watson (Jude Law) race to prevent the ritual murder of a woman by Lord Blackwood (Mark Strong), who has killed five other young women similarly. They stop the murder before Inspector Lestrade (Eddie Marsan) and the police arrive to arrest Blackwood.
In London, an unseen criminal begins masterminding his "perfect plot on paper" which starts with a robbery taking place and three cats stealing a pink diamond. Three constables spot them and give chase, but the cats escape to the rooftops and glide off into the night, giving the stolen diamond to a mysterious horseman. The next day Dr. Watson rushes to 221B in Baker Street and informs his colleague Sherlock Holmes of the robbery. Holmes calls Jerry Mouse to bring him a copy of the Times. Jerry heads out to buy it, bumping into Tom Cat on the way, who has something for Holmes. Jerry sends a pile of bricks on Tom and Tom gives chase. Jerry returns to Holmes' flat and hands him the paper or what was left of it after the chase. Reading a letter Tom had given to them, for the night, Holmes and Watson decide to go to the Bruce Nigel Theatre and see a lady named Red. Holmes is told that she is being blackmailed and Holmes suggests the perpetrator might be - Professor Moriarty. Holmes deduces that the Star of Punjab, a diamond that is sensitive to the light of a solar eclipse which was to happen the following day, is to be stolen by the mastermind of the blackmail.
In 1891, Irene Adler delivers a package to Herr Dr. Hoffmanstahl; payment for a letter he was to deliver. Hoffmanstahl opens the package, triggering a hidden bomb that is prevented from detonating by the intervention of Sherlock Holmes. Holmes takes the letter while Adler and Hoffmanstahl escape. Holmes finds Hoffmanstahl assassinated moments later. Adler meets with Professor Moriarty to explain the events, but Moriarty poisons and kills her — deeming her position compromised by her love for Holmes.
In London, circa 1897, a young mouse named Olivia Flaversham is celebrating her birthday with her toymaker father, Hiram. Suddenly, Fidget, a bat with a peg leg, barges in, and after a brief struggle, disappears with Hiram. Fidget takes Hiram to Professor Ratigan who commands him to create a clockwork robot which mimics the Queen of the Mice so Ratigan can rule England. Hiram initially refuses to participate in the scheme, but agrees when Ratigan threatens Olivia.
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.
The hero is Sigerson Holmes (Wilder), the younger and "smarter" brother of Sherlock "Sheer-Luck" Holmes. Envious of his more famous brother, Sigerson teams up with a Scotland Yard records clerk (Feldman) and a would-be opera singer (Kahn) to solve a case that Sherlock is unable to attend to, putting him up against both Moriarty (McKern) and a blackmailer (DeLuise).
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.
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.
Rio de Janeiro, 1886. Actress Sarah Bernhardt performs at the city's Municipal Theater, captivating the local audience enthralled by French culture. The city is at her feet, and even the Emperor Pedro II comes to pay his respects. He confides a secret to her: the disappearance of a precious Stradivarius violin presented by him to the charming widow Baroness Maria Luiza. The actress suggests to the monarch to hire her friend, the legendary British detective Sherlock Holmes, to solve the case. Subsequently, a brutal murder shocks the city, and leaves the police superintendent Mello Pimenta: a prostitute had been killed and mutilated, her ears cut off and a violin cord strategically placed on her body by the perpetrator. Later, under the heat of the tropical sun, the lives of Holmes and Doctor Watson are changed forever, as they find themselves neck-deep in a cultural milieu that portrays all standard Brazilian stereotypes.
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.
Les membres d'une société secrète londonienne succombent les uns après les autres dans de mystérieuses circonstances. Lorsque vient le tour du richissime Sir James Murphy, sa veuve désespérée fait appel aux services du détective Sherlock Holmes pour qu'il découvre ce qu'il est advenu de la fortune de son défunt mari...
Holmes and Watson are in Canada attending a conference on the occult, when Lord Penrose receives a message that his wife Lady Penrose has been murdered in the small village of La Mort Rouge. Holmes and Watson are about to return to England when Holmes receives a telegram from Lady Penrose, issued before her death, asking for help as she fears for her life. Holmes decides to investigate her death.
Master criminal Giles Conover (Miles Mander) steals the famous "Borgia Pearl" from the Royal Regent Museum under the very nose of Holmes and Watson, but when caught the pearl is not found on him and he is released.