Whilst on a week's secondment to Scotland Yard's Art and Antiques Squad, Lennox is tasked with investigating a young woman, Tessa Gannon, who tried to sell a forged painting to a gallery. Lennox soon finds a receipt from a gallery owned by an art dealer named Ivor Gregory, who has form for deception. Lennox befriends an artist named Richard Townes, who charges into Gregory's gallery as Lennox peruses the paintings. In the hope of getting a closer look at one of the paintings, Lennox arranges for his wife Shona to buy one of them. He gets it verified, and is disappointed when it is an original. When the painting is returned for re-framing, Lennox realises Gregory has swapped it for a fake.
