Orson Welles as Sigsbee Manderson is found shot dead in the grounds of his Hampshire country estate. The Record newspaper dispatches its leading investigative reporter, Michael Wilding as Phillip Trent, to cover the story. Trent manages to get past the police cordon and speak to Sam Kydd as Inspector Murch, the detective leading the investigation.
At the inquest, John McCallum as John Marlowe testifies that Manderson gave him instructions to go to Dover to meet a man named George Harrison. Manderson said he would travel with Marlowe as far as the golf course and walk back to the house for some exercise. That was the last time Manderson was seen alive. Marlowe claimed he continued on to his destination, but the police had been unable to trace Harrison.
The coroner's verdict is suicide. Trent, however, is convinced it was murder and persuades his editor to let him pursue the story.
At first, Mrs Manderson gives Trent permission to investigate. John Marlowe prepares to leave and Mrs Manderson tells him they should not see each other again. Trent continues his investigations. Mrs Manderson changes her mind and asks her uncle, Miles Malleson as Burton Cupples, to persuade Trent to stop investigating. Trent says his investigation is complete. Trent, by now in love with Mrs Manderson and aware of her husband's cruelty, visits Mrs Manderson and hands over his final report. He says he will leave it up to her whether to send the report on to his newspaper. She does not send it.
Several weeks later, at a concert in London, Trent meets Mrs Manderson. He tells her that suppressing the report has been a weight on his conscience. She says she understands, if she and Marlowe were lovers, and Marlowe shot Manderson. She tells him the truth: a week before her husband died, they had been due to go to the theatre, but he was delayed and John Marlowe took her to the theatre instead. During the evening, Marlowe realised that Manderson saw them, and his jealousy drove him insane, which is why he shot himself.
Trent is not convinced. At a meeting with Burton Cupples and Marlowe, Trent outlines, in detail, the circumstantial evidence that indicated Marlowe murdered Manderson. Marlowe then explains why he is completely wrong.
It was true that Manderson had given Marlowe instructions to meet George Harrison. It was also true that Manderson feared Harrison would not be in Dover, and that if he was not, Marlowe must continue on to Paris posing as Harrison to deliver an envelope. It was also true that Manderson accompanied Marlowe as far as the golf course. After Manderson exited the car, Marlowe had doubts. He opened the envelope Manderson gave him and found money and diamonds. He realised Manderson was framing him and intended to ruin him. Marlowe turned the car around to confront Manderson, only to find him lying dead on the ground. Marlowe's gun lay beside him.
Knowing he would be the obvious suspect, Marlowe decided to create an alibi by impersonating Manderson's voice so staff would hear him talking on the phone. He then continued on to Dover, though he knew it was a futile trip.
Trent believes Marlowe. It is assumed that Manderson killed himself with the intention of laying the blame on Marlowe. However, Cupples later confesses that he encountered Manderson while out walking on the golf links that night. Manderson had the gun in his hand and a strange look in his eye. Cupples attempted to wrest the gun from him, but it went off, killing Manderson. The pair had had an altercation in the hotel earlier that day, and Cupples feared he would be accused of killing Manderson deliberately because of it. So instead of contacting the police, he said nothing.
