Tommy and Tuppence are hired by Monty Jones to help him win a bet he has made with Una Drake. She has bet that she can produce an unbreakable alibi that will put her in two places at the same time. She subsequently provides him with information that puts her dining alone in a posh London restaurant and at a hotel 200 miles away in Torquay on the same evening. Visiting the London restaurant, the headwaiter vaguely confirms that she is a regular and that she very likely was in the restaurant on the evening in question. When they visit Torquay, they find the hotel receptionist, waiter and room maid all remember her quite well. When an acquaintance of Drake's is killed, our intrepid detectives wonder is there is perhaps another reason she wanted an airtight alibi.
—garykmcd