In a therapy session with Dr. Lee, Britten mumbles frantically. He was with his son and Emma at an LAPD fundraiser carnival. After getting talked into bungee jumping, Britten felt dizzy and fell off the platform, then woke up in Hannah's world. After taking Emma for a sonogram in the morning, Britten and Vega investigated a man on a killing spree. Since his victims seem random, Britten surmised the guy was out of his mind. After going to bed that night, Britten woke up in Hannah's world again - which has never happened before. Usually, it's Hannah, Rex, Hannah, Rex, just like clockwork. When Lee asks Britten what he thinks this means, Britten demands Lee help find a way back to Rex - now!
Dr. Lee finds this all to be positive news, a sign of progress. Falling is one of the most common ways to wake up from a dream. He's not telling Britten his dream is over - it's Britten's subconscious telling him. Britten won't believe it. Why would his dream stop now? Something must be wrong. Lee suggests Britten's life is starting to feel full again in a way that is helping him let go of Rex, who clearly died six months ago.
After his session, Britten climbs into his car, only to be surprised by a seemingly friendly guy he doesn't know, sitting in the back seat. Britten recalls bumping into the guy at the carnival with Rex, but this guy has no recollection of anything - not his name or what he's doing in the car, nothing. He's a figment of Britten's imagination. Britten asks if this has something to do with getting back to Rex or about his murder case, and the guy doesn't know. He's in Britten's head. He can only say what Britten tells him to say. Britten tries to put the pieces together to figure out why he's imagining this person. How is he connected to anything?
Britten makes Vega re-interview co-workers and neighbors about their killing spree suspect, Petroski, hoping it'll trigger something. He tries to ignore the guy from his car, who's now popping up wherever Britten goes. Britten describes his imaginary friend to the witnesses as someone Petroski may have known, though no one remembers anyone fitting his description. Vega reminds Britten of the time he kept looking for a "little guy" with no rhyme or reason for his actions; this seems like a similar wild goose chase. As Vega continues lecturing, Britten blacks out and recalls scenes of the crash with Hannah and Rex. Why did he flash back to the accident? Rather than allow Vega to call the paramedics, Britten asks to be taken home.
Over dinner, Emma mentions her mother cried to see her sonogram photo; however, her father Joaquin still seems to be having trouble with Emma's decision to keep the baby. Hannah asks Britten to try talking to Joaquin again, dad to dad. Spying the guy lurking in a corner, Britten consents, then retreats to bed, claiming that he's not feeling well. The next morning he wakes up in Hannah's world once again - and the guy's still there! At work, Vega and Britten find a realtor friend who let Petroski crash at his place. Vega sneezes during the interview due to the cats in the house. When Britten's imaginary friend begins sneezing uncontrollably as well, Britten investigates the table he's standing next to. Dust and droplets indicate something has been moved recently. Petroski figures it was probably his listing of vacant foreclosure properties. Vega is mystified; how is Britten finding these clues?
Police charge into one of the vacant houses to apprehend Petroski. During the interrogation, Petroski claims he's sick. He keeps having these thoughts and he doesn't know what to do about them, saying, "You don't know what it's like not being able to control what's in your own head." When Britten asks if Petroski knows anyone who looks like his imaginary friend, Vega immediately calls Britten into the hall. The suspect has already confessed - why is Britten planting ideas about other people being involved? Vega sends Britten home. He'll finish with Petroski alone. Back at home, Britten is surprised to find he's alone, no imaginary friend.
Once again, Britten wakes up in Hannah's world. Distraught, he staggers to Rex's room, only to find his imaginary friend sitting at Rex's desk. There's no reason for him to be there - the murder case is closed! Why won't this guy let Britten get back to Rex? The guy explains once again that he knows only what Britten knows. Maybe Dr. Lee is right. Maybe this is all there is now. Britten is stubbornly asserting that he won't allow for this just as Hannah walks in. Who's Britten talking to? Does he remember he's meeting with Emma's father today? Britten tries to postpone the conversation as his nerves are shot, but Hannah insists a guy-to-guy conversation could really help the situation with Emma and her parents.
After insisting that his imaginary friend remain outside, Britten meets Joaquin at a coffee house. While her father rattles on about Emma's naivete around motherhood, Britten is clearly distracted during the talk by his imaginary friend. When the guy shouts that he can see himself out the window, Britten sees the real version of his imaginary friend get into a car and drive off. Britten leaps up and charges out of the coffee house. Running through the street after the car, Britten manages to cause a different car to crash into a fire hydrant. While standing the street, Britten blacks out, flashing back to his family crash again. A few seconds later, Britten revives to find his imaginary friend luxuriating in the spray of the fire hydrant, while Joaquin demands an explanation. Claiming he has to pursue a suspect, Britten jumps in his car and flees the scene.
Back at the station, Britten sits with the composite sketch artist to create a sketch of his imaginary friend, whom he now knows to be a real person. Vega tries to cut in, but Britten yells at him, "Not now!" The sketch artist recognizes the man in the drawing as a detective at the West Bureau, Ed Hawkins. He's currently partnered with Britten's old partner... Bird! Has Britten finally found his "little guy"? Britten meets with Bird and Hawkins and can't help but awkwardly ask if he and Hawkins have met before or worked on a case together. Realizing Britten doesn't remember, Hawkins explains he was one of the first on the scene at Britten's accident. Britten goes home and thinks back to crash again. This time in his memories, Britten recalls seeing Hawkins after being pulled from the car by the paramedics.
Hannah comes home to find Britten sitting against a wall sobbing in the depths of despair. He explains that he finally realizes Rex is gone, and he blames himself for being behind the wheel. "I took our boy away." Hannah senses Britten was trying to stay so strong for her that he never had a chance to grieve for himself. The next day Captain Harper is forced to suspend Britten for his irrational behavior, pending an investigation of his actions. Britten leaves his badge and gun on her desk, telling her, "I killed my son. You can keep them." Afterwards, Britten visits Rex's grave and is shocked to spy imaginary Hawkins, who still has no idea why he's there. When Britten pleads with him to go, Hawkins disappears. That night, Britten takes off the red wristband he's worn to help keep track of his two worlds, knowing he won't need to use it anymore.
A teary eyed Britten visits with Joaquin again and apologizes for his actions when they last met. Maybe Emma and the baby have reawakened his thoughts of Rex. Losing a child is the worst thing ever to happen to him, and he wouldn't want another dad to voluntarily make the same mistake. Britten would give anything for one more day, hour or second with his son. Joaquin can hate Emma's decision, or the baby, or the Brittens, but none of it matters. Regardless, Joaquin should just hold Emma tight and not let her go, because... you never know. Joaquin gets the message and calls his daughter.
As Britten falls to sleep, he returns to his scattered flashbacks of the accident. This time he sees something new: a car knocks him off the road - driven by none other than Hawkins! When Britten wakes up, he's back in Rex's world, lying on a mat at the carnival's bungee jump. Elated, Britten gives Rex an exuberant hug, explaining he thought he'd never see him again. Britten looks around the carnival, spying the familiar police faces: Vega, Bird and Harper; with his new revelation, they all seem suspect. Later that night, Britten calls Dr. Evans. He needs to talk something through, and she's the only one he can trust. As a preamble, he explains that he got stuck in Hannah's world, which he thought was because he needed to finally accept Rex's death. Now he knows there's a totally different reason... another cop was trying to kill him. Dr. Evans agrees to meet in half an hour.