British Security is alerted when astronaut Peter Bourne suffers two assassination attempts, intended to look like accidents. After Bourne is blasted into space to place a top-secret device in orbit, detective Simon Brand is summoned to investigate, and to protect the device from being stolen. But then Bourne's spacecraft loses radio contact ... When it returns, the pilot is dead -- murdered whilst alone in space, and in a sealed ship! So begins one of Brand's most baffling and dangerous cases.