The Isle of Must lies two hours off the east coast of Scotland. Home to thousands of birds, a lighthouse, a bird observatory, a dog called Bess, a recalcitrant nature reserve manager called Fraser, and his assistant, Lefty, who isn't supposed to be there at all. And now it's home for Rachel, fresh from Norwich, armed with waterproofs and a desperate need to escape from her messy past a humiliating affair with her boss and also from the raw emotion that has followed her one selfless act: that of being a surrogate for her older sister, Lucy.