In the hopes to make detective, Brian volunteers to take an undercover assignment in a joint operation with the FBI and the LAPD. Under the alias, "Brian Earl Spilner", Brian is tasked with mission to solve a series of semi-trailer truck hijackings that occurred in the span of four months. Under Special Agent Bilkins and LAPD Sergeant Tanner's advisement, he was to find the persons responsible before the trucker drivers began to arm themselves to defend the merchandise they were carrying. However, their only lead was the description of the vehicles used: black Honda Civics with green neon under-glows.
Brian establishes a habitual lifestyle under his alias as an employee at The Racer's Edge, working for a man named Harry. For three weeks, Brian worked at the Racer's Edge and visited the Toretto's Market & Cafe, searching for an in. During that time, he tried to befriend Dominic Toretto's sister, Mia, an employee at the store and ordered what was considered an awful tuna sandwich every time he visited.
Brain visited the Toretto's market again and ordered the same awful tuna sandwich. When Mia questioned why he continued to do so, he merely tells her that he liked it. His repeated visits and flirting with Mia brought him to blows with Vince, Dominic's childhood friend. Dominic breaks up their fight, when Brian tries to protest being banned from the market, Dominic unilaterally declares that's he been fired from The Racer’s Edge. Following unceremonious termination, Brian purchases Nitrous Oxide from Harry in preparation for the street race later that night.
At the street race, Brian offers up his pink slip as an entry way into the quarter mile race Dominic is participating in. Dominic and the other racers oblige him. During the race, Brian manages to beat one of racers, but overwhelms his 1995 Mitsubishi Eclipse and almost loses control of the vehicle. When he arrives at the finish line, Brian boasts that he almost had Dominic, but the veteran racer believes otherwise.
Before their conversation can go any further, Leon warns the participants that the cops were on their way. Brian manages to escape the area without being detected and presumably follows Dominic. Dominic is pursued by the police after hiding his car. Brian follows him down the alley and offers him a ride. Dominic and Brian are able to avoid the police without major incident. Dominic tells Brian that he may have earned his "good graces", but would not be keeping his car.
Moments after their escape they are pulled over by Johnny Tran for entering his territory. Dominic covers for Brian, explaining to Tran that he was his new mechanic and didn’t know about the treaty between them. Unmoved by Dominic’s tale of accidental trespassing, he declares that Dominic's recently won Eclipse belongs to nobody and destroys it. On the hike on back to Dominic's House, Brian and Dominic talk about his sorted history with the Trans. When Brian prepares to leave Dominic’s house, Dominic invites Brian into his home to cause discord between himself and his group. Dominic uses Brian as a way to berate his crew who “left” him to the cops after they escaped the race. He offers Brian Vince’s drink just to irritate his friend. When Brian, Leon and Vince prepare to agitate Brian more, Dominic’s sister, Mia, decides to pull him away from the group and they talk. She offers him a place to sleep at their home and a shower. The following day, Brian is presumably heading back to The Racer’s Edge when he is pulled over by Tanner and his subordinate, Muse, who pretends to arrest him. They return to the penthouse where they talk shop with Bilkins about the progress of his investigation into Dominic’s link to the truck thefts.
In order to keep his promise to Dominic, he asks Tanner to provide him with a car. Tanner gives Brian a 1994 Toyota Supra MK IV, which he provides to Dominic in light of the destruction of the Eclipse. Brian begins to help Dominic and his crew restores the car. While running with Dominic, he proceeds to investigate rival race crews led by Johnny Tran and Hector.
Dominic's friend, Vince, rightly deduces that Brian is a cop, but Brian is able to convince Dominic otherwise by showing him what Johnny Tran is up to in his garages. In the company of Dominic and his friends, Brian grows closer to his sister, Mia, who becomes more aggressive in her interest in him whenever Vince tries to belittle him on account of Dominic’s obvious favor toward him. Tanner and Bilkins begin to fear that Brian is "going native" on account of the time he is spending with Dominic and Mia.
In order to set him back on track, Tanner shows Brian the records accounting Dominic's assault on a former racer, Kenny Linder. Brian promises to close the case soon and returns to Dominic's fold. When Dominic learns that Brian intended on taking his sister out, he threatens to "break his neck" if he hurt her. Brian assures Dominic he has no intention of harming his sister, and Dominic decides to show Brian his father's 1970 Dodge Charger R/T. He explains how his father died and what led to his attacking Kenny Linder, the man who caused the accident that killed his father.
Brian is pressured by Bilkins to arrest Tran as the likely suspect in the truck thefts. Reluctantly, Brian goes as far as to organize and lead a large SWAT team into Johnny Tran's and Lance's homes after finding large amounts of merchandise, the kind from the highway robberies, while infiltrating his garage. It turned out the merchandise was purchased legally and they find nothing on Tran except a few minor offenses. In light of his failure, it left Dominic as the only suspect, as Tanner predicted from the beginning. Desperate to close the case, Brian asks for an in on Dominic's side business; knowing that his market and garage businesses weren't the only way he was making money. Dominic agrees to let Brian in on his side business if he won races at the Race Wars event.
The following day, the consequences of Brian's actions against Tran come to fruition. Johnny accuses Dominic of selling him out to the police, following his race with Jesse, who left the event after losing his race against Tran. After Dominic is pulled away from attacking Tran, he and group part ways. Later that night, Brian searches for Mia and spots her in the middle of a heated argument with Dominic. When Dominic departs, Brian tries to get Mia tell where her brother went. Mia remains silent until he exposes himself as an undercover cop.
In light of the relationship they were slowly starting establish, Mia considers everything he’s done with her and her family a betrayal. Brian manages to convince her that if he does not get to her brother and his crew fast, they could be killed by the truck driver who is likely carrying firearms for protection.
Brian uses his serial number to ascertain information on Dominic's cellphone number and location. Brian and Mia arrive on the highway Dominic and the others are as robbery fails. Brian and Mia are able to free Vince from a wire attached to the interior of the truck and barely escape being shot by the driver. Brian reveals his identity as police to Dominic in order to save Vince from fatal injuries. When Vince is airlifted to safety, Brian is left out in the deserted highway by Dominic and Mia, who leave with Leon and an injured Letty Ortiz.
Using the Supra, Brian is able to arrive at the Toretto House before Dominic and leave to find Jesse. He tries to reason with Dominic, asking Dominic to let him call in the plates on Jesse's Volkswagen Jetta. The police would bring Jesse in before Tran and Lance can find him. Jesse appears before they can decide on anything, frantically apologizing for his actions. Tran and Lance drive by on their motorbikes and fire on the Toretto house, narrowly missing everyone there except for Jesse, who is killed.
Brian pursues Tran and Lance in his Supra, with Dominic following behind. Dominic is able to run Lance off the road just as he prepares to shoot Brian from behind. Brian continues to pursue Tran through the city until he fatally shoots him. When he confirms Johnny is dead, he chases after Dominic. When he finds him, Dominic has stopped at an intersection. He tells Brian he plans on crossing the quarter mile to escape when the light turns green.
Brian follows after Dominic as a train approaches. Both cars narrowly miss being hit by the train as they jump the tracks moments before the train passes them. On the other side of the tracks, Dominic's Charger is hit by an oncoming truck and tumbles across the street. After surviving his car rolling over, Brian helps Dominic out of the wreckage. He gives him the keys to his vehicle, reminding Dominic that he owed him a ten-second car. Dominic and Brian leave the scene as the police arrive, going in opposite directions.