It's peaceful in a canyon high above Los Angeles... until tires screech, and a car hurtles down a hill to land upside down, its three passengers unconscious. Detective Michael Britten of the LAPD is recounting the instant when his life changed forever to his new, department-mandated shrink, Dr. John Lee. Britten doesn't want to start with the beginning of this story; he wants to start with right now. He's back on the job, working with a new, young partner, Detective Vega, who Britten thinks has been assigned to make sure he's okay. And yes - he is okay. Cut to a crime scene, city street, rainy night. A cab driver has been shot. Witness Mr. Weaver, who lives in a nearby building, didn't actually see the crime, but did see a guy run into an alley. Noticing a surveillance camera on a nearby building, Britten sends Vega to get the tape. When Vega tries to thank Britten for getting him promoted to detective, Britten insists he didn't request Vega. The higher-ups probably didn't want to waste anyone else's time babysitting him after the accident.
After work, Britten goes home to his wife Hannah, who's decided to repaint the whole house... which she started doing right after the death of their son Rex in the car crash. Britten tells Lee that he goes to work, goes home, then wakes up to a whole different reality. In this world, his teenaged son Rex is alive; Hannah perished in the crash, and his psychiatrist isn't Dr. Lee, but Dr. Judith Evans. Britten tells her that Rex has ditched football for tennis after Hannah's death, probably because Hannah was so good at it. Evans notices that Britten wears a green rubber band on his wrist. He explains that it helps keep his worlds straight. Green is Rex's favorite color, and he wears a red rubber band for life with Hannah. In Hannah's world, Britten still works with his partner of many years, Isaiah "Bird" Freeman, and Vega is still in uniform. At present, they're at the swank home of Tom and Irene Baker, who have been stabbed to death in their kitchen.
The Bakers wallet and purse are gone, as is their BMW - and their daughter. After poking around, Britten declares the girl was in the house at the time of the murder. When Bird looks perplexed, Britten explains he can smell fresh urine in her closet, so she must have pissed herself while hiding there. Back in session, both therapists are fascinated by Britten's story - neither has seen a coping mechanism like his. Britten insists both his worlds feel equally real - which puts his therapists in a tizzy. They think Britten has constructed an elaborate dream - does he know which state is a dream? Is he awake or asleep? Britten crankily asserts that he does know when he's asleep; he just wakes up with either Hannah or Rex, but never both together. When Evans assures him that "this is not a dream," Britten laughs ruefully. Lee told him exactly the same thing...
Britten and Vega scan security footage, which has recorded a guy in a cowboy hat shooting the cab driver, then turning to look right at the camera - as if he meant to. Their viewing session is interrupted by the announcement that there's been another cabbie murder. Bird (in this world, Britten's ex-partner) is on the scene to inform that after shooting the cabbie, a heavyset guy with a beard and ball cap melted into the crowd. Britten is already looking for a surveillance camera, so Bird hands him a recent still - once again, the killer is facing the camera. When Vega leaves to take witness statements, Bird tells Britten the captain is moving him to the Western Division and calling it a promotion. He figures the captain doesn't want the two of them anywhere near each other - that's why they installed Vega to watch over Britten's shoulder. Britten better watch his step, because his behavior is definitely being scrutinized.
Lee reminds Britten that his office is a safe place, and doctor/patient confidentiality applies. Britten knows this is not quite true; his job depends on Lee's evaluation notes. Lee insists he can help - but not if Britten won't let him. Britten admits that at first, he told Hannah everything he was experiencing in Rex's world, hoping he might be a bridge between them. But to Hannah, Rex is dead, so hearing about him was more torture than comfort. Hannah is painting the house in preparation to move because, according to Lee, she's actually processing Rex's death in an effort to move on. Perhaps Britten can't understand this because he wakes up to Rex every other day - and that's the way he likes it.
At the precinct, Britten learns that a stolen car was retrieved in the Bakers' neighborhood, the most likely transport for the murderer to the crime scene. Neighbors saw the car as early as 5:00 p.m., but time of death was probably 9:00. Why wait so long? Britten's surmise - the killer was after the girl, so it's really all about abduction. He must have known the family routine. Britten and Bird decide to run a search on all registered sex offenders. Britten begs off to attend Rex's tennis match, sitting in the stands with Rex's coach Tara, who admits she used to play doubles with Hannah. Britten's surprised to see Rex is extremely good at tennis, and hear that he's been confiding in Tara about his mother's death. Rex slays his opponent, and after his winning stroke, he falls to his knees, crying. Britten runs onto the court, but it's Tara that Rex reaches for. The three of them go out for a bite afterwards. Britten has to cut it short when Bird calls him back to work. Although Rex feigns immunity, it's clear this scenario is a frequent disappointment for him.
Britten finds Bird at the Waverly long-term parking lot, standing beside the Bakers' stolen BMW, which is filled with and surrounded by blood. They must have missed the killer by about 45 minutes, but techs have taken photos while it was drizzling, revealing dry parking spaces. The killer must have driven his car to the lot, stolen one to get to the Bakers, then brought the girl back to the lot in the BMW, which was parked in space 589. Britten notices that the space directly behind 589 - 611 - is also dry, so they should find that driver. Maybe both vehicles left at the same time, and someone saw something. Bird doesn't think this is sound reasoning, so Britten offers to call the Bakers from home.
It's morning and Hannah's heading out early, reminding Britten they have a dinner date that night. At work, Britten tells Vega to pull the surveillance tapes, even though they've watched them 100 times. Britten's thinking their cab killer is loving the camera and the fact they still haven't caught him - he's probably in the crowd, watching them fail to find him. Maybe the same face will pop up on the videos after both murders in the crowds. In the meantime, techs pulled a single red hair off a discarded beard and wig near the scene of the second murder. Vega pulls up the tapes saying, "First up, 611 Waverly." Britten sits upright - this number corresponds to the parking lot space in the case he's working with Bird! When Britten tunes out to contemplate this anomaly, Vega can only wonder if the pressure's getting to him.
Lee thinks it's perfectly reasonable that things in Britten's worlds are crossing over, but Britten wants to know how he could have dreamed one 611 Waverly before the other. Maybe it's repeating to tell him that something important is going on? Reiterating that there's no world in which Rex survived the accident, Lee makes a very convincing case. That night, Britten is relieved to meet Hannah for their dinner date and surprised to learn that not only has she quit her job, but also she applied for a job in Oregon. Rather than get into it, Britten compliments her persuasiveness and asks if she wants to order wine. Hannah prefers to go home and make love. Afterwards, she divulges that she wants to get pregnant, and it's not about replacing Rex. Britten promises to sleep on it, then lets it slip that he saw "this kid" play tennis the other day. It doesn't take Hannah long to know he's talking about Rex, and she's deeply hurt. She too refers to Britten's "dreams," reminding him Rex is gone. When she asks if his psychiatrist is helping, Britten admits he feels better every time he opens his eyes.
Dr. Evans notes that Britten suddenly seems concerned about what's real and what's not. He admits Lee said a few things he's having trouble with. Evans wants to know why Britten might create a therapist who's so confrontational. He explains Lee would say that the reason Evans is gentle is because she is Britten. Evans prints out some text from her computer and hands it to Britten. After he picks a random spot and reads aloud, she asks whether he has memorized the Constitution. He hasn't - so how can he be dreaming right now? Shaken and agitated, Britten admits he can't explain it. That night, he's reluctant to go to sleep, and the next morning, when he wakes up without a rubber band on his wrist, Britten freaks out. Unable to find either Hannah or Rex, his panic escalates. Finally, just as he's cutting into his palm with a jackknife, Hannah appears, and he crumbles into her arms. In the calm that ensues with Hannah's first aid, Britten spies his red rubber band twisted in the bed sheets.
Britten stands in the street staring at the 611 Waverly building where the first cabbie was killed, annoying Vega. Why are they here? Britten says it's because of a dream, or maybe he's dreaming, then tries to dismiss his comment, but Vega heard it. Finally, Britten remembers Weaver, the witness. He said he saw the killer run down the alley, but Britten realizes Weaver couldn't have seen that from his apartment. And someone's in that apartment right now. The partners spring into action, entering the building. Britten just misses Weaver as he enters the elevator in another disguise. Britten pulls his gun and runs into the street, unaware that Weaver's approaching him from behind with a gun. Luckily, Vega is a quick draw and takes Weaver down with two bullets. Afterwards, Vega questions Britten's comment about the dream. Though he gets no answers, Vega promises that although he's been asked, he hasn't said anything about Britten to anybody.
In the green reality, Britten behaves much the same, dragging Bird to the Waverly parking lot to stare at space 611. Checking the parking space photos again, Britten decides the two cars in the adjacent spaces left at exactly the same time because they were hitched together. Maybe one of them was a camper? It's not long before Bird has coalesced some data. Four sex offenders in the area have campers, three of which are sitting in their driveways. The fourth just turned up by a lake in the foothills. When Britten asks if the guy has red hair (like Weaver) Bird looks at him sideways before they head up to find the camper parked in a remote campground.
Backed up by uniforms, Bird and Britten approach the trailer with guns drawn. Britten sneaks up to a window to spy the Bakers' daughter bound and gagged inside. He signals to her to stay quiet, then starts lifting out the glass window panels as Bird trains his gun on the big redheaded dude inside cooking sausages. When the dude hears something, he picks up his knife and charges for the girl, so Bird discharges his weapon. Afterwards, Bird demands to know how Britten knew the guy had red hair. When Britten claims it was a hunch, Bird explains he's been a cop for 20 years and has only seen hunches on TV.
In another session, Lee explains that Britten's mind will hop endlessly between his two possibilities - if he lets it. Britten has created a mental Mobius strip - how's Lee supposed to help? Britten insists he never said he needed help - the cops did. When Lee points out that Britten's blood alcohol level was elevated on the night of the accident, Britten insists he didn't have anything to drink. Evans is also concerned about this, since it does raise a lot of questions. Again, Britten insists there's no way he drank that night, and no, he still doesn't remember what led up to the accident. She postulates that his dreams may be a way of helping himself to remember what happened the night of the crash. Britten tells both Lee and Evans the same thing: although he sees both his wife and son in life, he has also seen both of them buried. And when you see that, the one thing you know is that you would do anything, anything at all to change it. So if the price of having both of them in his life is his sanity, he'll happily pay. That night in bed, Hannah asks Britten if he'll be seeing Rex tonight. Will he tell Rex that she loves him?