Two cousins, Toby and Cat(riona), are annoyed when Miranda, a London cousin, arrives at their island in Scotland for the summer. After preliminary snarls, the three become involved in a mysterious puzzle with occult overtones. Carrigona, the island, is a seal-nursery; the seals are connected to St. Culzean and their ancestors, especially Malise and his granddaughter Lucy. Lucy's portrait, with its piercing eyes, provokes the teens; Miranda's singing (during which her hands look strangely like Lucy's) unsettles the seals -- they leave the island for the first time in centuries. A young pup remains, wounded, and he becomes a household pet, diverting the teens to more earthy pursuits. But there is a serious threat for the seals -- they've moved to an unfriendly island -- which adds some suspense. Eventually the seals return, but only after Miranda turns against her country cousins and looks for adventure elsewhere.