At the start of the 1957 movie “The Three Faces of Eve,” the British-born journalist Alistair Cooke, who narrates the film, appears on camera to tell viewers that the incredible tale they are about to see is a true story — not suggested by or based on something that happened, but a facsimile of actual events.

Adapted from a book by two psychiatrists, Corbett H. Thigpen and Hervey M. Cleckley, the movie starred Joanne Woodward, who won an Academy Award for portraying an unassuming housewife who suffers from what is now called dissociative identity disorder, the psychological malady that manifests itself in the display of multiple personalities.

At the end of the book, and of the film, the title character, whose three distinct personalities were known as Eve White, Eve Black and Jane, was cured; the Eve personalities had dissolved. She was living as Jane, happily married and reunited with a young daughter from a previous marriage that had been irreparably rent by her illness.

In spite of Mr. Cooke’s assurances, however, the happy ending was premature. The patient whose story the book and movie purported to tell, Chris Costner Sizemore, actually had a much grimmer time of it. Her new marriage turned out to be not an ending at all; she endured a fragmented identity until the mid-1970s, seeing several psychiatrists after Thigpen and Cleckley, until, in the care of a Virginia doctor, Tony Tsitos, her personalities — not three but more than 20, it turned out — were unified.