Mirage (1965)

Walking down twenty-seven flights of stairs after the power goes out in the New York City office building he is in, David Stillwell emerges outside on the ground level to find out a man he did not know either jumped or was pushed out a window to his death. That man was Charles Calvin, the head of Unidyne, a humanitarian organization working toward world peace.

David notices other unusual goings-on. What he considers his normal routine others he knows should recognize, do not. People that he does not know seem to know him, such as the beautiful young woman with whom he walked down the stairs then ran off when they got to the bottom, and things he thought he saw or thought he knew end up not being the case, such as the multiple sub-basement levels he thought were in that office building which do not seem to exist in the clear light of day. When he finally thinks about it, he believes he has some form of amnesia. As an example, he knows he works as a cost accountant, but he has no idea what a cost accountant is or does. He soon learns some people are following him and are after something he has, although he is not knowing what it is, and they will shoot to kill if they do not get it. Conversely, the young woman, who he learns is named Shela and was once a love of his, is trying to convince him to cooperate with the people after him if only to save his life. Every direction David turns for official assistance, he comes up not trusting anyone, with the exception of a novice private detective he hires named Ted Caselle. Shela and the people after David all refer to "the major" as the person at the top who wants what David has. David may have to look deep into his troubled psyche to come out of his amnesia to learn who the major is, what he wants, whether David is willing to give it up if he indeed does have it, and if the death of Charles Calvin had some part to play. But David may be dead before he can even make an informed decision to cooperate or not.