The Intelligence Unit gets a call from AUSA Peter Stone when a key witness against suspected serial rapist and murderer Oliver Tuxhorn is found dead. Stone needs the team to find out who leaked the witness's identity and got him killed before Tuxhorn gets away for the fifth time.
Lindsay believes Tuxhorn is responsible but Atwater and Ruzek investigate a friend of Tariq's who called him the night he died and find a gun under his couch. The friend admits that they met but only to talk and that the gun isn't his. His alibi checks out, so how is the murder weapon in his apartment?
The team's investigation sends them to an ex-cop who's now working for Tuxhorn's lawyer. The ex-cop says Tuxhorn's brother Leo asked if he could get close to Tariq. Tuxhorn's sister Sloane starts looking guilty too when they find she made a $300,000 withdrawal from a family property in Dubai.
Sloane admits to getting the money but claims it was only a bribe. That sends Olinsky back to the ex-cop who swears the shooting was an accident, but Olinsky points out the cover-up was intentional and everyone gets handcuffs.
Meanwhile, Antonio meets with AUSA Stone as Stone has decided to make a change on his investigative staff in the wake of the incident. He even has Voight's approval to offer the job to Antonio. Antonio is resistant but accepts once Voight convinces him it's his time to be the boss.
And Burgess and Sorensen pull over an erratic driver literally wearing a chastity belt. But Sorensen thinks it'd be funny to upload the footage from his body cam onto Facebook which earns them the ire of Platt. Burgess admits she wants another new partner. But the episode ends with Lindsay and Halstead being pulled away from her mother by an "officer down" call.