A company director has been murdered by a perfect stranger. DI Alan Milton is put in charge of the case. He is the former fiancé of the victim's secretary. She is now about to marry a mysterious figure with a connection to the murder suspect.
Tom Fielding loses his secretary and needs a replacement, unfortunately Barbara Smith is one he should have avoided.
An old acquaintance of Milton's recounts how she overheard a conversation in which Fielding discusses his imminent death with Harry Brent.
Mrs Tolly had masked her identity, but her husband puts a devious plan in action in order to obtain Fielding's fountain pen.
Milton decides to share the discovered films with Carol, and a frank discussion forces him to confide in her.
Carol disappears after Harry explains what's going on, Tolly confesses to a little white lie.
Milton enlists Carol's help to set a trap for the killer.
