Jill Conway is a young Portland woman who lives with her sister, recovering alcoholic Molly. One year prior, Jill was kidnapped by a serial killer who abandoned her in a hole in the forest, where she found human remains. When her abductor descended into the hole to kill her, Jill was able to stab him with a bone and climb his rope and return to civilization. However, the police didn't find the hole and discovered that Jill had been committed to a psychiatric institution for several years after her parents' death. Believing that the abduction only happened in Jill's head, they closed the case.
One day, after returning home from work at a local diner, where she and her friend Sharon Ames are generously tipped by a regular customer about to move out of town, Jill finds Molly gone and is unable to reach her boyfriend, Billy. Knowing that Molly wouldn't leave the house with Jill absent and that she had an important test the following day, Jill becomes convinced that the man who took her has now captured Molly and heads to the police station to ask for help, but Sargent Powers and Detective Erica Lonsdale dismiss her claims and promise to look into the case after a few days, but Jill claims it will be too late then. Before she leaves, newcomer Detective Peter Hood pulls her aside and tells her he believes her, giving Jill his card in case she needs help.
Billy calls Jill and tells her that he hasn't heard from Molly, and that she didn't show up at the exam. Jill interrogates her neighbors and finds out a van with a locksmith's name parked in front of her house in the middle of the night and honked several times. Using the neighbors' description of the van, Jill finds the company it belongs to and heads there, where she questions the van's driver - who is also the company owner's son - about Molly's whereabouts. He claims to not know anything about it, and Jill feigns leaving in order to break into the van, where she finds a receipt for a hardware store and duct tape. She holds the driver at gunpoint and forces him to reveal that he allowed a stranger named "Digger" to rent the van the night before. Jill then leaves.
The locksmith's son reports this to the police, and Lieutenant Ray Bozeman orders Powers and Lonsdale to capture Jill, as she is a liability and has no permission to carry a gun. Hood tries to convince Jill to meet with him so he can help her, but she believes it to be a set-up so Powers and Lonsdale can arrest her and refuses. Meanwhile, Jill goes to the hardware store and learns from the owner that Digger's staying at a local rundown apartment named "The Royal Hotel". Jill heads there and learns from a neighbour his name is Jim Lapointe and breaks into his apartment, where she finds more duct tape, pet food (which she was given by her kidnapper), and matches from the diner where she works, the Lucky Star.
Jill visits Sharon and learns that Lapointe is the generous tipper from the night before. Sharon gives Jill his phone number and she leaves. On the way out, she's located by the police and chased to an alley, where she manages to escape and return to Sharon's house, where Sharon begrudgingly agrees to let Jill borrow her car. Jill then calls Lapointe, who confirms he's her abductor and implies he knows where Molly is. He orders her to go into Forest Park to find out the truth. Jill ignores the pleas of Powers and Lonsdale, who find her through Billy, and ventures into the woods, where she eventually finds the hole.
Lapointe emerges from a small alcove he dug nearby and throws Jill inside the hole, intending to kill her with a knife he carved out of the piece of bone Jill used to escape, but she draws her gun and shoots him in the chest.
Jill climbs back up and forces Lapointe to reveal that Molly was under their house the whole time, and he only used her to lure Jill into a trap. She then pours kerosene down the hole soaking Lapointe and throws a lantern left for her into the hole and burns Lapointe alive before returning to the city, where she reunites with Molly and tells her Lapointe is dead. Jill then lies to the police and tells them it was all in her imagination. They leave, and shortly thereafter, Jill sends an anonymous tip of where to find the hole, as well as pictures of Lapointe's victims that she had found near the hole. Bozeman calls Powers and tells him to re-open the case