In the premiere episode of “The Beast,” the mischievous Barker hazes Dove as they go undercover on their first case to infiltrate a weapons smuggling ring. Barker brilliantly manipulates situations, constantly tests his new partner’s abilities and pushes him to delve deeper into the roles of the undercover characters he creates. Although Dove takes a liking to Barker, the new job takes its toll on him. The stress and danger of being an agent quickly makes him realize that he can no longer maintain normal relationships outside of work. Yet that’s not the worst of it. The rookie is confronted with a larger challenge: An FBI Internal Affairs team feels Barker may have gone rogue and they try to enlist Dove as a double-agent in the bureau's investigation of his mentor.
Barker and Ellis are assigned to take down a major drug trafficking ring run by a man named Jimmy Casserly--who happens to be in the Chicago Police Department's (CPD) custody. Barker fears that if Casserly stays in CPD custody, his drug deal won't go through and they won't have enough evidence to lock him up for good. The partners come up with a risky scheme to bust Casserly out of CPD custody and all is going well until a major wrench is thrown in the gears--an ex cop with a personal vendetta is also chasing Casserly. Meanwhile, Ellis continues to burn the candle at both ends. He runs into Rose and she questions what he does for a living, and Ray from Internal Affairs tries to convince him that Barker is crooked by giving him a DVD with supposed evidence against his mentor.
Ellis and Charles take on a Romanian human trafficking ring. Charles goes undercover to take down the gang, while Ellis helps a Nadia, a prostitute who's son was sold on the black market by the trafficking ring.
Barker and Ellis get involved in a case dealing with millions of dollars and a deadly virus. The team discovers that a young boy has been given the virus as a means to blackmail his mother.
Barker and Ellis are tasked with keeping a top nuclear physicist alive and bringing her to the Nuclear Regulatory Commission to testify on a case. Meanwhile, Rose pays Ellis a visit at his apartment.
When suspicions arise that an FBI agent might have gone rogue, Ellis investigates the individual's ex-girlfriend and Barker gets close to him by going undercover at a security company.
A fellow officer has gone missing and is feared murdered; Baker goes undercover with a group of Latino drug dealers; Ellis works with the missing officer's partner.
Barker goes undercover as a homeless man to solve a series of murders of homeless veterans. The case hits Ellis particularly hard because he's a veteran himself. When Rose finds out that Ellis was in the military, she tries to get him to open up to her about his experiences, but the troubled Ellis turns her down.
Barker and Ellis work a case at a university where a Chinese spy is fronting as a professor. But finding the spy is not their only problem--an FBI agent doubts Ellis's ability and sets him up for failure.
Barker and Ellis infiltrate a high-stakes poker game to sniff out the assassin who's after an informant who's about to enter the witness protection program. Barker and Ellis have three tough jobs--protect the informant, figure out which player is the assassin, and not lose their $3 million buy-ins. Stars Patrick Swayze and Travis Fimmel.
Barker looks to take down an Irish crime family that controls a section of Chicago and is now expanding its empire to Wall Street. Stars Patrick Swayze and Travis Fimmel, and directed by Patrick's wife, Lisa Niemi.
After being set up for murder, Barker finds himself on the run and hunted by another FBI agent.
In the season finale, Barker gets a list of 6 people involved in Red Gauntlet. Now, Barker and Ellis, along with a little help, must take them down before they find Barker.