Atwater was working undercover at a drug syndicate to nab kingpin Darius Walker.
While working undercover, Atwater began picking up on Walker’s good deeds and wondered if maybe the dude wasn't as bad as he'd been led to believe.
But Walker's involvement in the drug business was still an issue. When two rival gang members ended up dead in a supposed retaliation against one of his men was murdered, Walker became a prime suspect.
Intelligence located a getaway car at the crime scene, which Atwater traced back to being the bartender at Walker’s bar, Nina.
Hoping to catch Walker in a deal red-handed, Atwater persuaded Nina to do some business with him.
Nina agreed to buy the product from his friend who was just Halstead undercover.
During the transaction, two men came in with their guns drawn.
Intelligence followed suit with their guns drawn and a screaming match of “put your gun down, this is the police” ensued.
Turns out, everyone was part of the police force.
Just like Atwater, Vanessa was working undercover as Nina.
Nina offered to go back undercover and bug Walkers' office.
While she's inside, he returned to find her in there.
Though he was suspicious, Nina played it off without raising much suspicion.
The next day, Intelligence decided to stake out the bakery where the alleged buy was supposed to go down.
They chased down a young kid whom Atwater saw communicating with Walker only to find out that the kid was helping deliver food to the poor.
They drove out to the other meeting spot right as the buy was happening.
As they attempted to take down Walker, the bust turned into a bloody and messy shoot out in the middle of the park.
Walker tells them that he wasn't responsible for killing the Latin Players.
Instead, he pointed the finger at their own leader.
He also managed to convince Atwater that he's good for business because people continue to buy drugs regardless of who is selling it.
If it isn't him, it'll be some punk who doesn't invest in the community.
Atwater understands and tells Voight that maybe they shouldn't arrest Walker.
Voight hears him out and turns to Interim Superintendent Jason Crawford.
He proposes that they let Walker walk so that he can continue contributing to the community and working for them.
Crawford likes that the proposition will make him look good and possibly land him the Superintendent job full time.
But there's a catch -- if Crawford agrees, Ruzek will be cleared of all charges.
Voight goes to Ruzek's house to give him the good news.
Ruzek is beyond grateful and breathes a sigh of relief.