Vere House, Hampshire, was once a peaceful have for Professor Martin Vere and his wife Diana until a series of minor thefts occur and the pair has to call in the help of undercover agent, John Mannering. What the couple don't know is that Mannering's expertise comes from his previous work as The Baron, a devious and deceitful jewel thief. When guest Lady Usk's famous Deverell necklace goes missing more help comes in the form of Chief Inspector Bristow of Scotland Yard. Mannering is immediately a suspect, made worse when he discovers the Deverell necklace in his own room.