Henry James's 1898 novella The Turn of the Screw involves a governess, whose job is to care for the rich indifferent uncle's niece (Flora) and nephew (Miles). The novella was brought to the big screen in the 1961 The Innocents, directed by Jack Clayton, which followed the book fairly well. As the novella and movie progress, the governess, Miss Giddens (played by Deborah Kerr in The Innocents), begins to see ghostly apparitions in the shape of a man (Peter Wyngarde) and later in the shape of a woman (Clytie Jessop). Yet, a person either reading the novella or watching the movie must question the governess's reliability. There is some difficulty in deciding whether the governess is actually seeing ghosts or just figments of her own imagination, but the question may be answered in three possible ways.
The first possibility is that the Miss Giddens has really seen ghosts. The only clear-cut evidence for this would be the great detail that she has in describing the male apparition, yet no other person in the Bly household can corroborate her sighting. The movie shows the ghostly apparitions, slightly blurred and with darkened lighting undoubtedly to enhance the scariness of the scenes. Yet, these ghosts probably are not really there in either case. Circumstantial evidence comes in when the housekeeper, Mrs. Grose (played by Megs Jenkins in the film), explains that the master's valet, Peter Quint, had previously died. One is also left to wonder why the governess does not bring a preacher in to perform an exorcism ceremony, rather than simply taking matters into her own hands. With little hard evidence that the ghosts actually did exist, this possibility cannot be conclusively proven.
There is another possibility that the "ghosts" she had seen are actually live people, perhaps people who live near Bly. They could have been neighbors seeking to steal something or even kidnap the children, Flora (Pamela Franklin) and Miles (Martin Stephens). Yet, there is even less evidence for this possibility than there is for the first. No footprints are found, the people seem to disappear, and apparently nothing comes up missing. Also, in the movie, the alleged "ghosts" seem to disappear into thin air after the sightings.
Finally, a third possibility is that the governess is utterly stressed out by her job of watching the children. She so fears that something really bad might happen to the children that her mind actually produces the "ghosts" in the form of hallucinations, which is common in cases of anxiety-induced psychosis. A vivid hallucination can be described in great detail, so the detailed descriptions of the alleged ghosts could have been explained in that manner. The scenes in The Innocents showing the ghosts could be argued as being shot from the governess's point of view, so they are likely to still be hallucinations that only she and the audience sees. The fact that the "ghosts" resemble Quint and Miss Jessel may have been simple coincidence. Further support for this possibility can be drawn from the governess's actions after seeing the ghosts. After seeing Quint's ghost, the governess becomes obsessed with protecting the children from the specters. She proclaims that the children have known about the ghosts but simply are lying about them. In the end, in both the novella and the movie, she even ends up literally scaring Miles to death.
There is little doubt that the ghosts in Henry James's The Turn of the Screw and Clayton's subsequent film, The Innocents, do not exist. It is unlikely that they are in fact real people either. Rather, it would seem that all of the ghost sightings, which the governess (and nobody else in the novella or play) experience, are in fact all in her head. She has been likely so stressed out by her job that her mind has produced very vivid hallucinations, which embody the fear of failure to protect the children as best she could.