Ivy and her twin sister Iris parents divorced when they were ten. Ivy got to live with their father and Iris went to live with their mother. Then their mother dies tragically when they're sixteen. After the death, Iris moves in with Ivy and their father. But she doesn't cry or mourn the death. Instead Iris seems to be only interested in Ivy's friends at school. Ivy feels something is off, but brushes it all off as Iris being traumatized. Then when her friends seem to turn against her, Ivy is determined to find out the truth. But will that be enough to save her?

What worked: Wowza, wow. Think Lifetime movie only with a more sinister undercurrent. I couldn't stop reading as I wanted to see what exactly Iris might be hiding. There's tons of psychological terror throughout this story.

Ivy is one of those overachievers and deals with anxiety. So when Iris starts acting one way in front of her and a different way with those around her, that anxiety is cracked up big time.

Slowly Iris plants herself in Ivy's life and not in a good way. It's not too obvious, but there are subtle hints throughout.

One thing that did bother me was how fast people were to believe Iris over Ivy. That includes their father. Iris is very manipulative and hides behind a friendly, concerned face. But I couldn't help but wonder why it was easy for everyone to get behind Iris. But other that that? This story is very compelling. I just couldn't put it down.

The ending has a mega sucker punch. I totally didn't see it coming.

Nail-biting thriller that will have readers second guessing themselves what's going on and ends with a chilling conclusion.