When the police knock on their door early one morning, Olivia and Park Bender are shocked to discover that DNA results show a wanted murderer is Park’s son. Impossible, they say, since they have been unsuccessfully trying to have children—until Park reveals he had been a sperm donor for a clinic in college.

Worse, the police reveal their discovery that Park has more children. Many more. The clinic had violated their promise to restrict the donations and dozens of children were conceived. Thanks to the proliferation of DNA tests, the kids have been finding each other and have formed a social media group to communicate with each other. They become aware that the killer shares their DNA—he is one of them.

As the police hunt the killer, they unearth more secrets from Park’s past. He’s connected to more than one fatality over the years, bearing uncanny similarities to the crime his son has committed. And Olivia has her own shadowy past, including a relationship with Park’s brother, Peyton.

When Olivia and Park discover the killer is following them, they fear for their own lives.