Ken Hughes directs this sci-fi mystery thriller. When a man is rescued from the River Thames after being shot in the back, the authorities are perplexed as to the man's identity. Luckily, reporter Mike Delaney (Gene Nelson) recognises the man as being Dr Stephen Rayner (Peter Arne), a visiting nuclear physicist who works at a nearby research institute. However, when Delaney finds Dr Rayner alive and well at his work, the real mystery begins. What is the true identity of the imposter recovered from the Thames?