To say Sgt. Hank Voight (Jason Beghe) has changed since he was first introduced on the third episode of Chicago Fire would be a massive understatement.

Intimidating and aggressive, he clashed with clean-cut firefighter Casey (Jesse Spencer) when Voight's son's DUI put a man in a wheelchair for life. However, as Voight's appearances on the series grew in number, and as the possibility of a Chicago P.D. spinoff loomed larger, the writers worked to redeem the seemingly dirty cop. They showed he was lying because he was working undercover for internal affairs. He was only aggressive and unrelenting because he truly cared about putting the bad guys behind bars. And lo and behold, Voight has now been the leader of Intelligence Unit, and the leading man of Chicago P.D., for three seasons and counting.

But as showrunner Matt Olmstead tells The Hollywood Reporter, "the old Voight" is about to make a comeback in Wednesday's season finale.

"As opposed to a whodunit, this is an absolutely gut-wrenching episode and Voight is put through the wringer emotionally and by extension, the other characters are too," Olmstead says. "It's Voight being, slowly over the course of an hour, being turned inside out."

Once again, Voight's son Justin (Josh Segarra) is to blame for his extreme behavior. Despite seeming to get his life back on track by enrolling in the Army and settling down with a wife and a kid, Voight recently learned his son is back in the Windy City. But although he told his dad he was bad to help a friend, Voight soon learns otherwise when Voight finds that Justin has been shot. "We have a Voight that is hell-bent," Olmstead says. "[He's] a guy who is completely blinded and will do anything legal, illegal. If I have to pay money, I will. If I have to pull a gun, I will. He's cautioned by people upstairs and he says, 'You'll have to put a bullet in my head to stop me.' He's just going 100 miles an hour looking for who did this to his son, which affects everyone."

Lindsay (Sophia Bush), is also impacted because of her teenage years spent growing up in Voight's house alongside Justin. "[She] is trying to prevent Voight from doing anything that is going to get him fired or killed or otherwise," Olmstead says.

Voight's right-hand man Antonio (Jon Seda) will be tested as well. "He's torn because Voight was there for him when Antonio's son was kidnapped and so he was beneficiary of a Man on Fire-version of Voight, yet now there are things that Voight does that perhaps Antonio might find infallible," Olmstead says. "So you have everybody at once concerned for Voight, sorry for Voight, worried that, are they going to get sucked down the drain if Voight gets sucked down the drain for improper police techniques?"

But after three years of trying to mold Voight into a good guy and leading man, why the sudden change of direction?

"I'm not sure which one's the tail and which one's the dog in terms of whether it was realizing, 'Hey, you know what? He's rehabilitated his character, he does a good job, and its time to show the fangs, or if it's we just knew that this event would be good storytelling and bring great conflict and energy and emotion and that it would require Voight to show his fangs again," Olmstead says. "But it accomplishes both."

Considering his character's dark introduction, Olmstead says it was only a matter of time before Voight took another walk on the wild side. "You can't white-wash his past completely so every once in awhile you got to show that he did time, that he did do some crazy stuff and also he is capable of something that most cops aren’t," he says. "You can't do it all the time, but its nice."

One thing's for sure: Justin's fate not only leaves questions about Voight's future but the future of the entire Intelligence Unit going into season four. "The whole show is shot out of a cannon with Voight being the cannonball in terms of finding out what happened to his son, and it leaves us with whether the ramifications of those actions afterwards. What's going to happen to him? What's going to happen to the unit? What's going to happen to Lindsay? And we'll answer those questions in the next season," Olmstead says. "It's a very propulsive, emotional, tense episode of a father looking to find out who put a bullet in his son."

Chicago P.D.'s finale airs Wednesday at 10 p.m. on NBC.