Steven meets Martin (Barry Keoghan) at a diner. Steven seems to be some kind of mentor to Martin, and has bought Martin the watch that he was asking the anesthesiologist about. After meeting with Martin, Steven has dinner with his family. His long-haired son, Bob, asks if he can go to a party with his sister (Steven's daughter), Kim. Steven says he can go if he cuts his hair. Steven's wife, Anna (Nicole Kidman), says just to let him go. Steven mentions that he's been spending time with a school mate of Kim's, Martin, because Martin wants to be a cardiologist. That night, Steven and Anna engage in some weird sexual act where Anna poses on the bed for him and he starts masturbating before he gets up and starts kissing her. The next night, Anna and Steven go to a gala where Steven is speaking. There, Steven gives his speech, and then we find out he doesn't drink when he is offered a cocktail.

Steven invites Martin over for dinner. At this point is you start getting a vibe from Martin that he's actually really creepy and weird. We find out that Martin's father was in a car accident and died ten years earlier so now it's just him and his mom living together. Martin hangs out with Steven's children in Kim's room, and he asks them about themselves. We find out that Kim is in a choir. Kim and Martin go on a walk together, and she sings for him in front of a tree while he sits and watches. Kim and Martin begin to develop feelings for each other. Later, Steven is driving through the parking structure at the hospital and sees Martin following him. Martin asks Steven to come to dinner at his house. Steven obliges. While they're eating dinner, Martin tells Steven that after dinner, he'd like for them all to watch his and his father's favorite movie. So they do. It's Groundhog Day. Martin says he's tired so he gets up and leaves, leaving Steven alone with his mother (Alicia Silverstone). She mentions that she knows her late husband was a patient of his, and she remembers him from when she went to the hospital after the accident. She says Steven has beautiful hands and begins to kiss them and suck on his fingers and Steven gets up and leaves. A day or two later, Steven and Anna are at a BBQ at his anesthesiologist's house, and Martin calls Steven. Martin is at the diner where they usually meet and wants Steven to come meet him, but Steven says he can't.

The next day, Bob is running late for school. Steven goes in to tell him to get out of bed, and Bob says he can't. He can't stand up because he can't feel his legs. He is taken to the hospital, and they run a full neurological examination on him before determining that nothing is wrong. He can walk again, and is walking out of the hospital with Anna when he collapses. He can't feel his legs again. The next day, Martin is there to visit Bob in the hospital, and Bob doesn't seem jazzed about it. Martin tells Steven to meet him in the hospital cafeteria. He tells him not to stand him up again. In the cafeteria, Martin tells Steven that because his father died on Steven's operating table, he sees him as his dad's killer. He says because Steven killed a member of his family, he'd now have to kill a member of his own family to balance it out. He tells Steven that if he doesn't, his family will all die the same way. First, by losing the use of their legs. Second, by refusing to eat to the point of starvation. Third, they'll start to bleed from their eyes. After that, it will be mere hours until they die. We see security escorting Martin out of the hospital after that. Steven goes to see Bob and asks him to eat some of his favorite donuts that Anna has brought for him. Sure enough, he refuses to eat.

Later, we see Kim at choir practice where she collapses during a rehearsal of Carol of the Bells. She ends up in the hospital in the same room as Bob. She too refuses to eat. The hospital continues to run tests on the two of them and determine that according to the tests, there's nothing wrong with them. Steven tells Anna about what Martin told him. She asks him if he had been drinking the day that he operated on Martin's father. He says it's possible, but a death on an operating table is never the surgeon's fault, it's always due to a mistake by the anesthesiologist. Anna meets with the anesthesiologist, and he says he remembers Steven having two drinks the morning before operating on Martin's father. He says when someone dies it's never his fault, but the fault of the surgeon. He then makes Anna give him a handjob as payment for the information he provided. A day or two later, Anna is at the hospital with her children when Kim gets a phone call from Martin. The two have been seeing each other since they first met. He tells her to stand up and come to the window so she can see him in the parking lot. All of a sudden, she's able to stand up, and she goes to the window but doesn't see him. She starts going back to her bed, and her legs stop working again the second she hangs up the phone. A decision is made to have the children come home instead of having to stay in the hospital. Anna goes to see Martin. He tells her that he thinks Steven killed his dad and Anna asks why she and her children have to pay for Steven's mistake. He doesn't answer but says that ever since his dad died Steven has been flirting with his mother and that he thinks they would be perfect for each other.

With the children home, we find out that they know about the decision Steven must make and they all start trying to flatter him to avoid having to die. Bob cuts his hair himself and says he wants to be a cardiologist. Later, Steven takes Anna down to the basement where he has Martin taped to a chair with cuts and bruises all over his face. He beats Martin to try to get him to make it stop. At night, when everyone is asleep, Kim drags herself down to the basement and asks Martin to let her walk again so they can run away together. Steven and Anna wake up and notice that Kim is not in her bed and they check every room, and she is nowhere to be found. They go down to the basement, and she's not there either. Steven asks Martin what he did to her. They start driving around the neighborhood and eventually find her dragging herself along with her knees/legs bleeding. Back at home, Steven tends to her wounds while she apologizes for going down to see him. The next day, Anna says she has set Martin free, and then Bob's eyes start bleeding. It is now time for Steven to make his choice. He tapes up his family members and puts pillowcases over their heads and then seats them in the living room. He stands in the middle of them with a rifle and pulls a beanie down over his face before spinning in a circle and firing the rifle randomly. He does this a few times, only hitting furniture in the house, until the final time when we see blood begin to stream down from under Bob's pillowcase. In the next scene, Steven, Anna, and Kim are eating in the diner where Steven used to meet with Martin. Martin walks in and sits at the bar and looks back at them. The family gets up and leaves.

End of the movie.