Katie and Adam are a young married couple struggling to pay their bills. Katie is working nightshifts at a diner while Adam is studying. One night, they are making out in their car during Katie’s break. They go back into the diner to find an armed robber threatening the staff. Adam sneaks up on the robber and knocks him out. He is hailed a hero while the robber goes to jail.
Four months later, Katie is working as a caregiver for Leonard, an elderly wealthy man who grows close to her. Adam has quit college and is trying to find a job that pays well so they can pay off their debt. Leonard tells Katie he keeps hearing noises in his house during the night.
One day, Katie tells Leonard about her financial struggles. Leonard insists on helping her out with money, but Katie asks him to give Adam a job as his gardener instead, which he does. The garden has been a mess since the last gardener stopped showing up one day. An insistent real estate agent, Hayden, appears and asks if he can buy the house. Katie refuses. Unbeknownst to Katie and Adam, Hayden starts to observe them on a regular basis.
Soon after, Leonard writes Katie a $7,000 check. Katie does not want to accept it, but Adam convinces her to use the check to pay the bills that are due and pay the rest back to Leonard. The next day, they arrive at Leonard’s home to find him dead, leaving Katie devastated.
The couple also finds a trunk full of cash. Adam wants to take the money and Katie reluctantly agrees so they can pay off their debt. They inform the police of Leonard’s death and are questioned by detective Chesler. When Adam goes back to the house to obtain the money, a mysterious intruder knocks him out, but doesn’t find the cash. They decide to put it in a safety deposit box.
At Leonard’s funeral they meet his attorney, Julia, who tells them about his will. Katie has been left everything, and the couple subsequently moves into the house. While Katie is reluctant to accept the inheritance and is worried someone might find out about the money they hid, Adam becomes increasingly greedy. He dreams of expensive vacations as well as luxury items and contemplates dodging the death tax.
Hayden reappears and threatens Katie, insisting that he must buy the house. She harshly refuses. As Adam comes back he tells her that he believes he is being followed, Katie realizes that Hayden is after them. Detective Chesler becomes suspicious of Adam and starts to investigate the circumstances surrounding Leonard’s death and the robbery at the diner.
While exploring the living space above the garage, Katie finds a body with uncashed checks written to Leonard’s previous gardener, Ethan Doyle, who apparently died from a gunshot wound several months ago. She also finds a bag of diamonds on the body. Katie wants to call Detective Chesler, but Adam convinces her to keep the diamonds. He dumps the body and burns all evidence of Ethan’s existence.
Detective Chesler suggests to Katie the possibility that Adam and the shooter at the diner knew each other, since he worked at the university Adam was attending. Katie becomes increasingly suspicious of Adam, especially after finding an empty bottle of pills that wasn’t accounted for in the logbook of Leonard’s medications. She meets with Julia to discuss a course of action. Julia warns Katie about Adam betraying her and says the police are about to obtain a search warrant on her house. When they inspect the safety deposit box, the money is gone. Julia suspects that Adam took it and is planning to run away, leaving Katie as a suspect in Leonard’s death. She tells Katie to get him to the house and call her.
When Katie confronts Adam about the money, he tells her he found out that Hayden is actually a jewel thief who was recently released from prison, and not the real estate agent he portrayed himself to be. They realize that Ethan was Hayden’s partner in crime and Hayden killed him to get his share of the diamonds. Ethan, mortally wounded, fled to Leonard’s house where he died. Hayden knows the diamonds are hidden somewhere in the house and is eager to find them. Adam convinces Katie that they must leave. Katie agrees.
While Adam is getting ready, Katie calls Julia to tell her Adam wasn’t planning on leaving her. Her call is interrupted when Hayden shows up and holds Katie at gunpoint, asking for the diamonds. Hayden and Adam exchange gunfire and both are killed. Katie rushes to Adam’s side, the last thing he says to her is “in the garden” before he dies of his wounds.
Suddenly, Julia arrives. Katie tells her that Hayden was the one who killed Leonard, giving him an overdose of his medication. She also tells her that Leonard claimed he heard someone in the house at night, who must have been Hayden breaking in and searching for the diamonds. Julia reaches for Hayden’s gun and holds Katie at gunpoint, revealing that she is part of the plot. She had met Hayden during her public defender duties and orchestrated everything, including Leonard’s forged last will, to get a share of the diamonds. She demands the diamonds but Katie tells her Adam hid them somewhere and she doesn’t know the location. Detective Chesler arrives in time and shoots Julia.
Four months later, Katie is shown to be pregnant and gardening outside. Chesler tells her that the case is closed and that Adam would be kept off of the list of suspects, keeping his reputation and memory intact. Chesler talks about how they searched the house top to bottom for the diamonds but never found anything. Once more, Katie tells her that she still has no idea where the diamonds are. In the last shot, Katie turns the sprinklers on and leaves the garden. The water moves the soil aside and the diamonds are shown to be buried under a tree, making sense of Adam’s dying words.