Jim Dixon feels anything but lucky. At the university he has to do the bidding of absent-minded and boring Professor Welch to have any hope of keeping his job. Worse, he has managed to get entangled with unexciting but neurotic Margaret Peel, a friend of the Professor's. All-in-all, the pub is the only friendly place to be. His misery is completed at a dreadful weekend gathering of the Welch clan by the arrival of son Bertrand. Not so much that Betrand is loud-mouthed and boorish - which he is - but that he has as companion Christine Callaghan, the sort of marvellous and unattainable woman Jim can only dream about.

When Professor Willingdon becomes wary of the nuclear weapons he is helping build, he steals a warhead and threatens to detonate it in London in seven days unless the government begins nuclear disarmament. As Willingdon goes into hiding, Detective Folland of Scotland Yard sets out to find him. Willingdon's daughter Ann also joins the cause, hoping she can talk sense into her father before he causes a catastrophe.