Mercy — Jodi Picoult

Police chief of a small Massachusetts town, Cameron McDonald makes the toughest arrest of his life when his own cousin Jamie comes to him and confesses outright that he has killed his terminally ill wife out of mercy.

Now, a heated murder trial plunges the town into upheaval, and drives a wedge into a contented marriage: Cameron, aiding the prosecution in their case against Jamie, is suddenly at odds with his devoted wife, Allie -- seduced by the idea of a man so in love with his wife that he'd grant all her wishes, even her wish to end her life. And when an inexplicable attraction leads to a shocking betrayal, Allie faces the hardest questions of the heart: when does love cross the line of moral obligation? And what does it mean to truly love another?