Charlotte Rossignol's great-uncle, the renowned archaeologist Alan Morris, disappeared over a year ago. When she visits his last dig at Aurae Phiala, a Roman site on the Welsh border, she meets the charming and knowledgeable Gus Hambro. Her suspicions of him flare up when he secretly slips out of the hotel at night. Following him down the river path to Aurae Phiala, she is just in time to rescue him from drowning after a murderous attack.
Detective Chief Inspector George Felse links the attack to the death of a schoolboy, Gerry Boden, who was last seen on the site after wandering away from a school party. On his body is a valuable gold coin apparently filched from a hidden Roman treasure hoard. Similar pieces have been appearing on the international antiques market for some time, and it seems possible that whoever has been concealing the discovery for personal profit is the murderer.
Charlotte is invited to stay with the curator and his young wife, personal friends of her great-uncle, while the police are examining the site for clues. Gus offers his expertise in preserving any artifacts uncovered during the search; he is again almost killed when a tunnel collapses on him. As he recovers Charlotte gets to know him better, becoming more convinced that he is not what he seems to be. When Gus sees a shadowy figure in a Roman helmet, he goes to investigate. The mystery of Charlotte's great-uncle is about to be solved.
This report prepared by Maureen Evans