The rookies have worked 100 shifts and on their 101st, it is Plain Clothes Day. Their Training Officers will be wearing plain clothes and will only be there to observe, not to advise, assist, or help in any way. 

Officer Jackson’s patrol car won’t start and he and Lopez end up stuck at the precinct for two hours while the battery is replaced. 

Then Detective Wolf, who is on desk duty and recovering from a gunshot wound since his partner was killed, pulls Jackson to catalog evidence in a homicide case of Richard Ochoa. Jackson is upset because he had wanted to beat his father’s record for number of arrests made during Plain Clothes Day. 

When Ochoa’s widow comes to the precinct asking if she can have some of her husband’s things back because she needs something of his to remember him, at first Jackson turns her down. Then, instead of heading out on the road, he goes back and finds a watch that can be returned. Lopez is proud of him when he decides the day has been a success instead of a failure.

Officer Chen second guesses many of her decisions during Plain Clothes Day with Bradford. When they are called to a home for a noise complaint about a barking dog, the owner is belligerent with Chen and repeatedly kicks dirt at his dog. Chen tells him that if he keeps it up, she’ll make him her personal project. The man calls in an official complaint saying that Chen threatened him. 

When Bradford goes back to smooth things over the man threatens to charge him with harassment. Bradford tells Chen they need to walk away, but she sees the dog trying to get into the garage and what looks like blood on the door. She insists on checking it out and finds the body of the neighbor who called in the noise complaint. She arrests the dog owner.

Captain Andersen tells Officer Chen that the complaint will be dropped but threats, even veiled ones, will not be tolerated in this precinct and if this ever happens again she will lose her job. 

Officer Nolan tells Bishop, who is in plain clothes, that his goal is to make detective in five years. He tries to drive up his felon arrest rate by running license plates at a local motel. He gets a hit on one and calls in backup but only manages to frighten a mother with a baby who bought the vehicle three days earlier. 

A woman in another motel room tries to ask Nolan a question about being tracked through her credit cards but he’s so focused on making arrests that he gives her a card with a number to call and blows her off.  

Bishop reaches out to Detective Wolf to make sure he’s doing okay but he misinterprets it and hits on her. He realizes his mistake and tries to make up for it by giving Nolan a warrant for a felony arrest. On the way to the arrest, a call comes in about a disturbance from the motel. Nolan decides to respond to that call first.

The woman who spoke with Nolan earlier, Lynn McDaniels, has been abducted by her estranged husband. Nolan and Bishop find his truck and trailer, in which he’s holding Lynn with both a knife and a gun. Nolan and Bishop manage to disarm him and save Lynn. 

Later, Bishop tells Nolan to stop looking at his age as a weakness and to see it as a strength. That he has empathy for people and that can’t be taught and the only way to make detective is to just be him.