Antonia is a secret Silver Dolphin – she's responsible for helping the creatures of the bay when their environment is threatened, by responding to the call of her magic necklace.

A new girl, Emily, joins Sea Watch but Antonia instinctively feels wary of her. Emily's parents have just set up a tourist beach shop selling dried starfish, shells and sea urchins, and Antonia can't quell her suspicions that they have been raiding the bay for these spoils. But when a baby dolphin is caught in a net, Antonia discovers there's more to it than first appearances suggest…