Is there someone out there who looks just like you? Could a person be in two places at once? The infamous Dr Jekyll/Mr. Hyde is perhaps one of the most famous examples of the doppelganger (double walker), in which an individual is either split into two or more contrasting personalities, or is haunted by a "shadow" figure that may or may not be a repressed part of himself. In Henry James's 1898 novella, The Turn of the Screw, filmed as The Innocents in 1961 by Jack Clayton, I believe Peter Quint (Peter Wyngarde) has his own "double walker," which accompanies him.
The story revolves around a young woman, named Miss Giddens and played by Deborah Kerr in the movie, who has recently taken the position as governess of two children, Miles (Martin Stephens) and Flora (Pamela Franklin). From the beginning, it is apparent the governess is smitten with her employer, the uncle, depicted by Michael Redgrave in the film); and, throughout the novella and film, she hopes to gain his respect or affection by succeeding at her job. However, she soon begins to struggle against two "evil ghosts" she encounters, whom she believes vie for the souls of the children. These "evil ghosts," the governess believes, are the tortured souls of Peter Quint and Miss Jessel (Clytie Jessop), the children's former chaperons.
When alive, Quint was handsome, but untrustworthy, and known for having multiple affairs with women, including Miss Jessel. He enjoyed wearing the master's clothes occasionally. As a ghost or possibly a hallucination, Quint appears to the governess multiple times and places ideas into her head that he wants Miles' soul.
According to http://www.webhome.idirect.com, a doppelganger is a shadow-self that accompanies every human. It almost always stands behind a person, provides compassionate company, and casts no reflection in a mirror. While a good listeners and great at giving advice, this doppelganger often implant ideas in human's heads.
Since it is said to be bad luck if a doppelganger is seen, and rarely does a doppelganger make itself visible to friends or family, does the governess simply imagine that she is seeing the ghost of Peter Quint because she could simply be mad and delusional, imagining ghosts and evil that are not there? Or is there a real one who is causing great confusion and mischief in the novella and movie? Either way, James and Clayton have created an ambiguous scenario that continues to fascinate the reader and viewer.