The Will Trent season 4 finale opens on a grim, chaotic note: a young man is peeing on a dumpster when a cop arrives, orders his three kids out of the car and then pulls a baton to swing at him. The scene cuts hard from that violence to the Team Law and Team Lab baseball game, where Will gets a strong hit before striking out and Seth catches the ball that gives the doctors the win.
By the time Will, Faith, Angie, Ormewood and Wilks get back to the precinct, the episode has already shifted from a game to a disappearance. Three friends are waiting at the elevator, pressing for answers about their friend Lizzie and saying she has been taken by the police, but there is no record of her in the system. Nick has also already been beaten badly after the officer hit him several times, and the kids say the officers just took Lizzie and left.
That is the point where Will and the others start to see the shape of the case. They conclude that the pair who took Lizzie were impersonating cops, not real officers, and the search turns to why she was singled out. Faith speaks with Lizzie’s parents and learns about a nurse who had been stealing pain medication and was fired after Lizzie’s father reported her, a detail that suggests the family may have crossed someone with access and a grudge.
The episode then tightens the evidence. Ormewood tracks down footage from the scene, and Wilks recognizes the uniforms as belonging to a TV show filming in the area. That detail closes the gap in the story: the people who took Lizzie were not police at all, but fake officers using a production uniform to make the abduction look official.
Season 4, episode 18 makes the answer plain. Lizzie was taken by impersonators, and the team’s job is no longer to ask whether the police did it, but to catch the people who used a badge-like disguise to make everyone believe they had the authority to walk away with her.