Ginger-haired Tom and his twin sisters Jill and Mary

are on holiday on the Scottish coast, in the fishing village where their best friend Andy, a fisher-boy, lives and works with his father. Their holiday plan is to take an exciting boat trip to a nearby island, and camp there, but once out at sea, their plans are turned upside down and they find themselves shipwrecked and in the middle of a thrilling and mysterious adventure...