Chicago PD Season 5 Episode 13 kicks off on a cryptic note — Voight is overlooking as the police find a body. 

He seems concerned enough to call Olinsky because "they know." In return, Olinksy promises to keep his ear to the ground for anything that might link him to the body.

It doesn't take long for Denny Woods to pop in and inform Voight that they've made a positive I.D on the body: it's Kevin Bingham. 

For those who don't remember, Kevin was the man who killed Voight's son, Justin. 

Woods knows that this is his hook on Voight, but he pretends to offer him condolences and some "closure," assuring him he'll get his best people to look into it. 

Obviously, a jab at Voight because HE DID it. 

Voight tells Olinsky to give Lindsay a heads up in New York. 

The case of the week finds Antonio's friend, Marco, a store manager, killed by a San Salvador gang. 

The murder gruesome was committed with a machete, as most of their murders are. 

They send out kids to collect money from local shops and if they refuse to pay, they get removed. 

Marcella, a visiting cop, lends her help to the case since she knows a thing or two about the gang unit. 

She quickly takes a liking to Antonio who isn't opposed to all the flirting. 

Unfortunately, he was simply being used as bait. Marcella wasn't just passively interested in the case; she came to Chicago with a purpose. 

Burgess was the detective who originally realized that Marcella was withholding information. Antonio was so blinded by her charms, and the fact that they slept together, he didn't even heed Burgess' warning. 

Burgess finally enlisted Ruzek's help and together, they figured out what Marcella was really after: El Lobo, the leader of the SS 11. 

Marcella previously told Antonio that he son was killed in a car accident. The truth is that he was killed by El Lobo and she joined the Salvador Vigilante squad and get her revenge on him for killing her son. 

Unfortunately, they pieced everything together a little too late and when they found El Lobo, they found Marcella with a gun to his head. 

Antonio pleaded with her, but Voight knew from experience that there was no negotiating with someone who wanted to avenge their son's death. 

Marcella killed El Lobo then pointed the gun at Antonio forcing him to shoot her dead. 

Denny pays Voight another visit before the episode's end to inform him that the FBI found evidence linking him to Kevin's murder— bullets from a gun he took from a victim that never made it into evidence.