Jealous that the waitress is beating her to the altar, Dee does everything in her power to derail the wedding. Meanwhile, the guys distract Charlie by getting him back in the dating scene.
The gang attends their high school reunion with a lot to prove. Old friends are met and new foes are made as the gang trips down memory lane.
In the conclusion of this two part episode the gang devises a new plan at their high school reunion to make sure their tarnished high school images will now sparkle and shine.
When a mutilated sex offender is found dead, it is unclear if he was the victim of a hate crime, sexual assault or self mutilation. As Intelligence questions those related to the case, they find themselves up against a private "special police" force who may be covering up illegal activities. Meanwhile, Halstead (Jesse Lee Soffer) runs Jimmy's (guest star Tony Crane) DNA to confirm that he is actually Lindsay's (Sophia Bush) father.
After the body of young woman is found with multiple gunshot wounds, Intelligence uncovers details of her case that are similar to other deaths. They work to link all of these murders together to pin down the serial killer, and appease the families of the victims who have been looking for answers. Meanwhile, Lindsay (Sophia Bush) decides to meet her biological father (guest star Tony Crane) for the first time, and Voight (Jason Beghe) welcomes Kenny Rixton (guest star Nick Wechsler) to the team when Ruzek (Patrick John Flueger) takes an undercover assignment.
