Hoping to escape his grief over the loss of his beautiful wife Heather, Michael leaves behind his New York precinct to embark on a police-exchange program. As a police officer in rural North Wales, he is struck by the tenacity and resourcefulness of Catrin, a single mother with a frightening past. It appears that her brother Seth is involved in drug dealing-and something much bigger. After Seth's sudden death, Michael is forced to overcome Catrin's hostility and her wariness to trust anyone, especially a man. Michael vows to protect her and her young daughter from the unknown assailants, and he and Catrin must decipher the meaning of the mysterious code etched on the back of a valuable oil painting. As the threats and terror escalate, Michael finds himself betrayed by those closest to him-even the Heather he remembers-and realises Catrin was right not to trust anyone. But when they are trapped in an underground cave with the tide rising, one of the people is their only hope for escape.