Don's team is charged with running VIP security for a big political rally featuring high profile activist Benjamin Polk. While scouting out the venue in preparation for the event, Don and his team come under heavy fire and receive a message to stay away from Polk during the rally. This overt attempt to scare Polk and the FBI away doesn't work, and Polk insists on keeping his speaking engagement at the gathering. The FBI then digs in to try and discover who is making the threat, and discover that it's a man who'd lost his son during a violent riot orchestrated by Polk to gain political street credit in order to further his own career. Furious that his son had been blatantly used as a pawn, the man, Shepard Crater, had come to LA to exact revenge. On the day of the rally Crater sets off a sequence of events to force Polk back to his hotel, where Crater is set to ambush and kill him. Charlie deduces the plot just in time, and David and Colby move in and take Crater down before he can kill Polk. However, after learning the whole story from Crater before they take him down, Colby and David meet with a political journalist and blow the whistle on Polk's tactics, effectively ruining his political career.
Charlie is still working on his letter to the following occupant of his office and Don is back at work after his stab wound. Don's team at the FBI is in charge of running VIP security for a rally run by high profile activist, Benjamin Polk. While the team preps for the event, with the help of Charlie's mathematical mock ups, they're fired on by snipers and receive a message to stay away from Polk during the rally.
Despite the attempted scare, Polk insists on keeping up the rally. Don's team begins to dig deeper to try and figure out who is behind the threat. They discover it's a man, Shepard Crater, who had lost his son during a riot that Polk had orchestrated in order to gain more political street-cred to further his career. Clearly upset that his son was used as a pawn, he came to Los Angeles to get revenge on Polk.
On the day of the rally, Crater sets off a chain of events which forces Polk back to his hotel room where he will wait to kill him. Charlie is able to figure out the plot in time and David and Colby are able to take out Crater and save Polk in time. All was not lost though, since Polk's political tactics were outed to a political journalist and his career essentially ruined. The team also receives great news that Amita has accepted Charlie's proposal and that they plan to get married.