At the emotional core of the novel is the complex and twisted relationship between Claire and Amber. Given the fog from which Amber only slowly emerges and given that her backstory is filled in from diary entries that may or may not have been written by Claire, the reader pieces together a disturbing picture of friendship used as a weapon, friendship that evolves into a dark and dangerous game of manipulation and emotional blackmail and ends in murder.

It is in its own way a cautionary tale about friendship that refuses boundaries. From the day Claire and Amber meet in elementary school when they are both 10, Claire feels a deep bond with this girl. Amber seems helpless, vulnerable, misunderstood, and weak. Their friendship evolves into a bond in which Claire feels compelled to protect Amber—at first from the mean girls who taunt her in science lab; then from her parents, whose reckless parenting and emotional indifference underscore that they never really understood her; then from a boyfriend who threatens her with his obsession; then from a husband who never appreciates her enough; and ultimately and tragically from Amber’s unborn child. Friendship here corrupts into possession, a sense of entitlement and ownership that Amber finally breaks when she is driven to poison Claire on Valentine’s Day after she understands that Claire, in the name of their toxic friendship, deliberately caused the accident that killed her baby.