When her daughter’s bestie becomes obsessed with her, a woman thinks it’s innocent until things escalates and she finds herself taken prisoner by the crazed friend who has convinced herself that she now has the mom she has always wanted.

Amy, a recent college graduate, has the best relationship with her mom Kate. While she moved out right away, Amy lives just down the street so she can see Kate as much as she wants. It’s the perfect mother/daughter relationship.

Heather, on the other hand, was always neglected by her drug addicted, alcoholic mom Tammy. Tired of her mom failing her, Heather kills Tammy and goes on living her boring life as an assistant librarian at the public library.

When Kate can’t go with Amy to find a new dress, Amy goes it alone and meets Heather. The girls hit it off, talking a lot about their moms. Heather wants what Amy has more than anything and sticks close to her new best friend. Going to Kate’s for dinner, Amy invites Heather to join her. Immediately, Heather is drawn to her friend’s mom, having more of an interest in Kate than she does in Amy.

Kate sees Heather as a lonely woman missing her mom, who allegedly died from a drug overdose. As Heather’s visits grow more frequent, Kate isn’t concerned. She even takes Heather to get a complete makeover that makes the Plain Jane into a beauty. The trouble really begins when Kate decides to go out on a date with a co-worker, Roger. Heather doesn’t want anyone taking Kate’s attention from her so she kills Roger the morning after he spends the night with Kate.

Since Kate spent her birthday having dinner with Roger, Amy plans to take her mom to dinner the next night. Heather arrives at the office with a diamond bracelet she bought as a birthday gift. Kate tries to refuse it but Amy is insistent. Then the news hits that Roger was found dead that morning. Kate is devastated by the news but keeps her dinner date with Amy.

Amy is already growing suspicious of Heather’s motives but when she sees the bracelet her mom has received, Amy is now certain that Heather has become unhinged. Kate blows it off as Heather missing having a mom and she’s going a little overboard. When Heather shows up at Kate’s office again, Kate starts to realize Amy is right. She asks Heather to back off some, a request that only causes Heather derangement syndrome.

After losing a chance at a big promotion, mostly due to Amy, Heather goes off the deep end. She kills her head librarian and kidnaps Kate, taking her to a remote farmhouse where she plans to make Kate into the perfect sitcom mom from the 1950s. Unable to escape, Kate is forced to play along while she plots. Amy keeps texting and calling her mom, irritating Heather. Pretending to be Kate, she tells Amy all is fine. She went off on a retreat and would like Amy to join her. When Amy arrives, she is also taken prisoner. Mother/daughter are forced to team up together to take Heather down while there’s still time, and hope that they can find a way to free themselves when no one knows where they are.