The film's plot has Sherlock Holmes and Dr. Watson attempting to recover a stolen necklace, formerly worn by Cleopatra, from Professor Moriarty. Holmes tries to convince the police that the professor is a criminal, but they are disbelieving.
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.
Cette série soviétique est particulièrement fidèle aux intrigues d'origine écrites de Conan Doyle, tout en mélangeant parfois deux intrigues dans un même épisode en créant de nouveaux raccords « extra-canoniques » entre deux affaires. Livanov joue un Sherlock Holmes assez décontracté et capable d'un humour discret, correspondant aux écrits de Conan Doyle.
The film begins with a title card describing Holmes and Watson as "ageless", as an explanation as to why the film is set in the 1940s rather than Holmes' era of 1881–1914, as the preceding 20th Century Fox films were. Though there is a nod to the classic Holmes in a scene where Holmes and Watson are leaving 221b Baker Street, and Holmes picks up his deerstalker. Watson protests, and Holmes reluctantly puts on a fedora instead.
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.
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.
Sherlock Holmes (Basil Rathbone) pretends to be a Nazi spy to aid scientist Dr. Franz Tobel (William Post Jr.) and his new invention, a bombsight, in escaping a Gestapo trap in Switzerland. Holmes and Franz fly to London, where Holmes places him under the protection of his friend, Dr. Watson (Nigel Bruce). The scientist slips away against Holmes' instructions for a secret reunion with his fiancee, Charlotte Eberli (Kaaren Verne), and gives her an envelope containing a coded message. He tells Charlotte to give it to Holmes if anything should happen to him. Leaving Charlotte's apartment, an attempt to abduct him by German spies is foiled by a passing London bobby.
When several women are murdered and their forefingers severed, Holmes and Watson are called into action, but Holmes is baffled by the crimes at the start. Widower Sir George Fenwick (Paul Cavanagh), after a romantic night alone with his girlfriend Lydia Marlowe (Hillary Brooke), is hypnotized into believing that he is responsible for the crimes. He is certain that he is guilty after he awakes from a stupor and finds a woman's forefinger in his pocket. His daughter comes to Holmes and Watson without realizing that Moriarty's henchman is following her. She tells Holmes and Watson that she found her father burying a forefinger under a pile of soil. She has dug up the forefinger and shows it to them.
Des meurtres semblables à ceux attribués à Jack l'Éventreur sont commis à Madrid. Holmes (Gary Piquer), qui est sujet à des rêves prémonitoires au cours desquels il entrevoit la survenue de ces meurtres, décide de se rentre à Madrid pour enquêter sur l'affaire en compagnie du Docteur Watson (José Luis García Pérez) marié depuis peu à Mary Morstan (Leticia Dolera).