Celebrating the end of exams with best friend Grace, 17-year-old Alex rescues a swan caught on a wire in the Thames mud and finds an extraordinary bracelet. Through its disturbing and compelling powers, she finds Callum, a soul locked in a half-life of sadness and mystery following a terrible accident, and his persuasive and sinister sister, Catherine. As Alex and Callum grow closer despite the enormous obstacles to their love, the dangers mount until Alex must risk everything to save Grace and Callum must risk everything to save Alex.