This week, Team Arrow has apparently prioritized the street gang the Culebras over the unsolved murder of their partner and friend, so Arrow, Dig and Roy investigate what else but a warehouse.
What they find there isn't an active gang; instead they find a pretty gruesome scene: what must be a dozen dead bodies strung up by their legs and a message that simply says "Guilty" written in blood on the floor. Arrow interrogates the one guy left alive, who tells him that a guy named Paco was involved.
Arrow goes to a bar and does his best Christian-Bale-as-Batman voice to ask the patrons about Paco. I don't know what happened to his voice-altering device in this particular scene, but he's really gruffing it up here. It's ludicrous. Anyway, a guy tells him that Paco is really a fellow named Emilio Ortega, along with where to find him.
Turns out that place is Wildcat's gym (where he's been training Laurel in boxing). Arrow finds yet another dead body there, so when Wildcat comes walking in, it's pretty incriminating. He's only saved when Laurel comes walking in behind him and establishes an alibi.
The police come and, after some formalities, decide not to arrest Wildcat. Ollie, who is super jealous, isn't so eager to let Wildcat off the hook. The killer is apparently left-handed, just like Wildcat, and the corpses are being hung from the ceiling, just like heavy bags! That is a real point that is made.
The victims are also being beaten to death with brass knuckles, which makes it even more incriminating when Arrow goes to Wildcat's secret shed and finds: 1) brass knuckles, 2) another dead guy and 3) weird newspaper clippings about the local vigilante.
After a brief fight, Wildcat explains that he used to be a vigilante just like Arrow, and that this is all some kind of revenge setup. Arrow rightly asks why he's never heard of Wildcat. Wildcat says he stuck to working in The Glades, so TV didn't pay attention to him. This is...highly dubious. Maybe he was just terrible at his job.
Either way, Wildcat says he's never killed anyone...except maybe one guy he may have beaten to death by accident six years ago. He's not killing these people, though.
So of course Arrow and Wildcat have to team up. They track the killer to a nightclub, where a masked assailant shoots at the heroes and openly talks about his shared past with Wildcat. It is very apparent he's Wildcat's old sidekick, but Wildcat tries to play it off like, "Who's this guy? What's he talkin' about?"
The killer escapes just as the cops arrive and arrest Wildcat for the murder of the body they found in Wildcat's secret shed (our heroes just left it there, I guess). In the interrogation room, Captain Lance says Wildcat is charged with 16 murders, "more than Son of Sam. That's a Bundy." That a hilarious way to count murders.
Anyway, Laurel gets Wildcat to admit that the killer is his old sidekick, Isaac Stanzler, who is not a comic character I'm aware of. Turns out Stanzler also killed that guy six years ago and Wildcat took the heat for it.
The cops drop the charges on Wildcat, and as he and Laurel are leaving police HQ, Stanzler sneaks up on them. He says he was captured by the Culebras and "tortured for months" after Wildcat quit the vigilante game. Wildcat apologizes and asks to talk. "I have so much to say before I kill you," says Stanzler, which is a pretty good line.
Stanzler takes Laurel and Wildcat hostage and makes her drive him...somewhere that doesn't really matter. Laurel secretly calls Smoak because Stanzler is super careless and didn't take her phone, tipping Team Arrow off to where they are.
Arrow catches up to them on his motorcycle in almost impossible time, but he goes down when Stanzler shoots out a tire. (Arrow also shoots an arrow directly into the car that should definitely have killed Wildcat. It goes right through the seat.)
Roy comes riding up and manages to get Stanzler out of the car while it's moving. Laurel crashes into some other cars. Dig and Arrow get her and Wildcat out just in time before the car explodes.
Roy and Stanzler fight for a while as Stanzler tells Roy that Arrow will abandon him, just like Wildcat did to him. Roy says he's not Stanzler and incapacitates him in an act of sidekick-on-sidekick violence.