This comes toward the end of Hammer's cycle of '60s psychological thrillers and while the formula must have been getting familiar at the time, seen in isolation this is still an entertaining suspense picture. Though characteristically implausible. Robert Webber is an American travelling through Europe who loses his memory in a car crash.
He discovers that someone is trying to manipulate his loss of identity and fit him up as the fall guy on a murder rap. These films all owe a debt to Alfred Hitchcock, as do most thrillers of the period. There's even a shower scene. And the credits are a tacky rip off of Saul Bass' for Vertigo. Though it most obviously takes its premise from Gaslight (1940).
Until... the customary big final twist. Webber is more of a tv actor, but carries off the hokum pretty well. The support cast is underwhelming, apart from Maurice Denham who is most enjoyable as an enigmatic, cranky private detective.
There's a sleazy/sexy jazz soundtrack, some swanky high life interiors and, as standard with Hammer psycho-thrillers, a gallery of arresting b&w images. It is expertly made. The story is slight so there is some padding. It won't change your life, but this is a lively, lowbrow escapism.