When a teen takes a pet sitting job for her new neighbor, she has no idea that he is arranging her disappearance to hold her prisoner in his bunker as a replacement for his deceased daughter.

Home for college, Emily Landen wants to enjoy her summer off from school at home with her mom Debra, her dad Jeff, and her younger sister Megan. When she wants spending money, Jeff tells Emily to get a summer job. Debra suggests pet sitting and has Emily hang up flyers around town.

After murdering a local woman who looked a lot like her deceased daughter Karen, District Attorney Sandra Meyer is on the lookout for the next replacement. She spots Emily hanging up a flyer and decides she looks almost like Karen and takes a phone number tab home with her. When Sandra’s remote neighbor, the sweet, elderly Charlie Wells, asks if she knows a pet sitter for his dog Sampson, Sandra recommends Emily. Charlie meets with her and hires the college student to pet sit during the upcoming weekend while he plans to go fishing alone.

Emily runs into an old friend from high school, Greg. They go on a date but have to wait for a second one because of Emily’s job. Alone and spooked at the remote house, Emily chats with Greg on the phone and invites him to come by later. Meanwhile, Sampson needs to go outside in the dark. Emily uses a flashlight to take him. Watching nearby, Sandra sets off firecrackers that spook the dog and send him into the woods. 

Emily gives chase. Sandra catches her off guard and uses chloroform to knock her out. After she plants Emily’s blood in the trunk of her car and inside Charlie’s house, she chains her up in her cellar and attempts to make her into her lost daughter. Emily tries to find a way out, but Sandra has thought of everything, and no one would suspect an outstanding D.A.

Greg goes looking for Emily and finds her broken necklace near Sandra’s house. As he moves in to investigate, Sandra knocks him out with a poker and throws him down the cellar steps. Although Emily pleads for Greg’s life, Sandra is enraged and kills him in front of her, after fracturing Emily’s arm.

Debra is frantic to find her daughter and confronts the detective in charge of the case, Ava Sanchez. Ava and her partner Ron tell Debra to back off and let them handle it. They arrest Charlie for Emily’s disappearance after the lab results show the blood found at the scene belongs to Emily. As Ava thinks more about the case, she starts to suspect Sandra, as both missing women look a lot like her deceased daughter. She goes to speak with Sandra at the same time Emily mounts an escape attempt.

Sandra is pushed into killing Ava to save herself. Emily gets free and stabs Sandra, then flees. She encounters Ron outside and waits in his car while he goes inside to get her abductor. After shooting him, Sandra goes after Emily. She fights back with a fury and returns to her family, and their newest members, Charlie and Sampson.