Cass Lynch is still staying aboard Khalida and her Norwegian shipmate Anders and his pet Rat seem to have settled happily into Shetland life too. Naturally, they take an interest in summer visitors, especially the friendly yachting couple who've come to Shetland for the archeology. They were going to walk up to the Trowie Mound, an unexcavated Neolithic chambered cairn - but when they don't return, and their yacht departs mysteriously in the middle of the night, Cass contacts old adversary DI Gavin Macrae, who takes advantage of his holiday to come up and investigate. He's got wind of art theft which seems to centre around Shetland - but how can this link to a ghost baby wailing from the island of Linga?
Then one of Cass's sailing pupils goes missing, and she has to risk finding out the secret of the Trowie Mound by herself ...
This fast-moving thriller brings back some characters from Death on a Longship, including Cass's old teacher Magnie, her friend Inga, and the engaging and mischevious Peerie Charlie. There's mayhem at the country show, and a nail-biting on-water finale with a final twist as you find out at last 'who-dunnit'.