The novel begins with a man confessing to the mercy killing of his wife who was suffering a painful and slow death to cancer. However, this man's story is second to that of the police chief, Cameron McDonald, who finds the love of his life five years after marrying the woman in his life. Cam is a man to whom responsibility is a suffocating burden he must bare. In rebellion against this weight, Cam breaks his loyalty to his wife and explores a relationship with a woman who has the freedom he craves. It is not until his wife learns of this affair that Cam finally realizes that he never really intended to leave his wife or the life they have built together. Mercy is a story of the tests that challenge people everyday and the mistakes that define a life.