Kal McKenzie always had a tricky relationship with her mother, Elena, but when Elena dies of breast cancer, Kal is bereft: how do you mourn a mother whose love you could never count on? While clearing out Elena's art studio, Kal finds a drawer packed with postcards going back thirty-seven years. Each bears the same message from a stranger called Susannah Gillespie, who owns a gallery on a remote British Columbian island, a place of killer whales and storms. On impulse, Kal sets out for Spring Tide Island with her toddler, Finn, in tow. Can her mother's hidden past hold the key to their ruined relationship? Once she arrives at Susannah's isolated home, Kal quickly realizes she has made a big mistake. The handsome and enigmatic Susannah is alternately elated and disturbed by Kal and Finn's arrival, and refuses to talk about her friendship with Elena. As Kal struggles to piece together what happened between the two women in this inhospitable place back in the 1970s, Susannah's behaviour grows more and more erratic. Most worryingly of all, Susannah is becoming increasingly preoccupied with little Finn . . .