Missy Peregrym portrays Andrea (“Andy”) McNally, the series protagonist.

She is driven by the desire to do the right thing even if it means not following procedure. Her father, Tommy McNally, was formerly a homicide detective before he burned out. As a result McNally carries her father’s baggage, trying to prove herself. Andy is the most positive person on the job—because she knows first-hand where the job can take you, and she does not want to go there. Her mother, Claire, is a social services worker who abandoned them when Andy was a teenager. She studied Sociology/Psychology before becoming a cop and she was an A student.

She begins a relationship with homicide detective Luke Callaghan, and the two move in together at the end of Season 1, although she previously kissed and almost had sex with Sam Swarek, her training officer, before walking out on him, something that leaves them in discomfort for several episodes. She later becomes engaged to Callaghan but breaks up with him after he slept with his ex-girlfriend, Detective Jo Rosati. She finally confesses that she has feelings for Swarek, but he has already left on an undercover mission. The last three episodes of season 2 show viewers the beginning of Swarek and McNally’s relationship, even though he is undercover, which leads them both to suspension for “conduct unbecoming” when they are discovered.

In the beginning of season 3, Andy returns from a trip after her three months’ suspension and gets her job back as well as restarting her relationship with Swarek. When her mother suddenly appears in her life due to a work case, she decides to let her back in after she asked for a second chance. After Detective Barber’s death, Swarek breaks up with her, which causes a lot of pain for Andy. After a month and a half, and in a life-threatening situation when she is holding a grenade, Swarek says to her that he loves her and then he tries to get her back. Then Detective Callaghan asks her to participate in a task force, which will keep her isolated and away from 15 Division during the mission. She accepts but has to leave immediately, which leaves Swarek drinking at the Penny (the local bar) while waiting for her.

In the first episode of season 4, when she returns, she finds out Sam has been dating Officer Marlo Cruz while she was gone. Later on, Nick confesses his feelings for Andy, and the two embark on a new relationship. When Sam gets shot in the season 4 finale, she goes in the ambulance with Sam, and then tells him she still loves him.

Hours late and Season 5 picks up in the hospital.