Under cover of being marine biologists on a UNESCO project, they travel in the Firecrest, an outwardly normal but very specially equipped motor launch.

His chief suspect is Cypriot shipping magnate Sir Anthony Skouras, whose luxury yacht, Shangri-La, is also anchored in Torbay.

But late at night, they are boarded by local police and plain-clothes men claiming to be customs officers seeking information on stolen chemicals.

On the promise of a share of the insurance reward, Calvert recruits the assistance of Tim Hutchinson, a shark fisherman who has unrivalled knowledge of local water conditions and boat handling.

Guessing that the missing bullion ships are being sunk to allow the gold to be offloaded invisibly, Calvert, formerly a marine salvage expert, dives into the bay and finds the Nantesville.

Calvert tells Charlotte that he didn't believe her story, and that he knew from the beginning that she was faking, with information received from Uncle Arthur.

Calvert is a typical MacLean hero, world-weary and sometimes cynical, yet ultimately honorable, who must battle bureaucracy as well as the bad guys to solve the crime.

Calvert's frantic search for the hijackers and for the hostages they hold takes him over the remote isles and sea lochs and forces him to make allies of some unlikely locals.