The first third of the film is told from the main character’s, Jean-Dominique Bauby (Mathieu Amalric), or Jean-Do as his friends call him, first person perspective. The film opens as Bauby wakes from his three-week coma in a hospital in Berck-sur-Mer, France. After an initial rather over-optimistic analysis from one doctor, a neurologist explains that he has locked-in syndrome, an extremely rare condition in which the patient is almost completely physically paralyzed, but remains mentally normal. At first, the viewer primarily hears Bauby’s “thoughts” (he thinks that he is speaking but no one hears him), which are inaccessible to the other characters (who are seen through his one functioning eye).
A speech therapist and physical therapist try to help Bauby become as functional as possible. Bauby cannot speak, but he develops a system of communication with his speech and language therapist by blinking his left eye as she reads a list of letters to laboriously spell out his messages, letter by letter.
Gradually, the film’s restricted point of view broadens out, and the viewer begins to see Bauby from “outside”, in addition to experiencing incidents from his past, including a visit to Lourdes. He also fantasizes, imagining beaches, mountains, the Empress Eugénie and an erotic feast with one of his transcriptionists. It is revealed that Bauby had been editor of the popular French fashion magazine Elle, and that he had a deal to write a book (which was originally going to be based on The Count of Monte Cristo but from a female perspective). He decides that he will still write a book, using his slow and exhausting communication technique. A woman from the publishing house with which Bauby had the original book contract is brought in to take dictation.
The new book explains what it is like to now be him, trapped in his body, which he sees as being within an old-fashioned deep-sea diving suit with a brass helmet, which is called a scaphandre in French, as in the original title. Others around see his spirit, still alive, as a “Butterfly”.
The story of Bauby’s writing is juxtaposed with his recollections and regrets until his stroke. We see his three children, their mother (whom he never married), his mistress, his friends, and his father. He encounters people from his past whose lives bear similarities to his own “entrapment”: a friend who was kidnapped in Beirut and held in solitary confinement for four years, and his own 92-year-old father, who is confined to his own apartment, because he is too frail to descend four flights of stairs.
Bauby eventually completes his memoir and hears the critics’ responses. He dies of pneumonia two days after its publication. The closing credits are accentuated by reversed shootings of breaking glacier ice (the forward versions are used in the opening credits), accompanied by the Joe Strummer & the Mescaleros song “Ramshackle Day Parade”.