The episode kicks off 36 hours before the Mayoral election. Internal Affairs is closing in on Ruzek; they know he's lying to protect someone in his unit following the suspicious death of a suspect who was pushed out of a window. 

Voight knows that if Kelton becomes Mayor, he'll not only disband Intelligence but he'll also pursue legal action. He reaches out to the "disgraced" Brennan to see if she'll help him nab Kelton. 

She shines light on one of his partners, his "fix it man," and a dangerous drug dealer. 

Atwater goes undercover thanks to his CI Maya to catch Wilson doing a sale while Jay bugs his vehicle. 

They follow Wilson around, but with time running out, Voight orders the team to do a dark bust in which they all go into the warehouse with their faces covered and ambush Wilson's men. 

With everything stolen, Wilson is forced to buy more product, and Intelligence hopes they can catch him during the transaction. 

But when they get on the scene, the seller begins unloading rounds at the undercover cop car.

Upton and Halstead take cover in each other's arms and miraculously come out unscathed. 

Wilson isn't so lucky. 

Kelton arrives on the scene furious and asking why Voight didn't change gears to a different case as he requested Intelligence to do. 

Voight brings in Trey, the suspect he believes is responsible for the shooting and puts him in the cage. 

He hopes he'll be able to scare him so he flips on Kelton, but Trey still refuses to talk.

With time running out, Voight cracks under pressure. 

He tells Ruzek not to take the fall, but Ruzek shakes him off. 

Antonio questions why he's doing this for him, so Ruzek informs him this is the only way he could live with himself. 

Halstead realizes something is up and corners Voight about it. 

Voight doesn't reveal the truth but tells Halstead that one day, Intelligence will be his to run. 

"Do it the right way."

Halstead is visibly confused but aware that something terrible is about to happen. 

As Kelton is elected Mayor of Chicago, Ruzek is arrested outside of the precinct. 

Platt walks him down and informs him to "keep his head down" as he assures her he'll be fine. 

Shortly after, Halstead, Burgess and Atwater respond to a shooting at the Mayor's house. 

They find Kelton dead on the ground from multiple gun wounds and immediately think Voight, who promised to take care of it, is responsible. 

However, we see Antonio cave under all the pressure and pop some pills. 

Who pulled the trigger?