Noah (Dominic West) and his wife Helen (Maura Tierney) have been married for many years. They have four lovely and lively children. They have been very happy in their marriage for a long time. Noah considers himself a competent husband and responsible father. He and Helen both think that the peaceful life will last forever. One day, a beautiful woman named Alison (Ruth Wilson) appeared beside Noah. Her beauty and intelligence made Noah fall into an immoral love affair and couldn't extricate himself. Alison is also a married woman. Her husband Cole (Joshua Jackson) is a cowboy who runs a farm. The relationship between Alison and Cole is already full of problems. Coupled with the unexpected love between her and Noah, the two families are pushed into an irreversible situation.