While walking home from an OB/GYN appointment, the very pregnant Esther Woodhouse (Alexia Rasmussen) is knocked unconscious by a person in a hoodie who proceeds to brutally bash her belly repeatedly with a brick. Despite the efforts of the ER doctors, the baby is already dead when removed by C-section. Noticing that Esther doesn't seem to have any friends or family (the baby was conceived via sperm bank), a social worker at the hospital forwards her to a support group for grieving parents.
In the support group meetings, Esther meets and befriends Melanie Michaels (Alexa Havins), a woman who claims her husband and child were killed by a drunk driver. Later on, while visiting a department store, Esther sees Melanie walking in alone and suddenly start screaming that her son Peyton was kidnapped and begging a security guard for help. Esther follows Melanie to the parking lot and witnesses her taking Peyton out of the car and into the store, presumably to be "found". Esther is strangely pleased by this.
While Esther is home, her "attacker" suddenly appears and is revealed to be her lover Anika Barön (Kristina Kleb) who has performed the attack at Esther's request. She asks about Melanie, clearly jealous but Esther dismisses her.
Esther later invites Melanie into her home. Esther asks about Melanie's family and she sticks to her drunk driver story. Esther then tries to seduce Melanie, claiming that she's the only person who understands her. Melanie rejects Esther and when the latter says she knows what happened at the department store, Melanie slaps her and tells her to never contact her again.
Esther takes Anika's truck and tracks down Melanie's house. Sneaking in with a crowbar, Esther finds Peyton in the bathroom and drowns him in the bathtub. Melanie enters and distraughtedly asks why Esther did this and she claims that she did "the things that [Melanie] couldn't do" and now they can be together. After she says this, Melanie's husband Patrick (Joe Swanberg) walks in with a shotgun and kills Esther.
Days pass and the Micheals' are heavily grieving. Patrick is particularly unhinged and fantasizes about having left Esther alive so he could torture her. After noticing Anika's truck and the fact that it hasn't moved ever since the murder, he enters it and finds the registration. However, when he reports it to the police, he is told to stop since it would constitute theft (even though the door was unlocked). Patrick also starts attending a support group but then finds out from a regular that his wife had been secretly attending for a year and that she had claimed Peyton was kidnapped. Patrick confronts Melanie who denies everything and apparently leaves her.
Meanwhile Anika, enraged by Esther's death, tries to track down the Michaels' and finds out where they are from the police informing her about her truck. She goes to Melanie's house, ties her up and plans to wait for Micheal, so she can torture and kill them both. She then hears running water from the bathroom and investigates, believe it's Michael taking a shower. Instead, she finds him dead. Melanie breaks free and holds Anika at gunpoint and thanks her, claiming she just made a "much better story".
We then see a clip where Melanie is being interviewed on TV two years later, having written a book about her experiences on having both her son and husband murdered and advocating for child safety. She also announces that she has remarried and is now pregnant...
...and this is revealed to be a fantasy of Melanie's. Anika manages to reach for a hammer and the movie ends with a gunshot on a black screen, the outcome unknown.