Malcolm (still John Barrowman) tells Moira that Doug Miller told him that Walter asked him questions that suggested that he's seen The List. That's an elaborate sentence, but it mostly covers things that we saw happen. The point is that Doug could tell that Walter must have seen The List somewhere. Moira complains about Malcolm menacing her family, but Malcolm points out, "Your family won't stay away from me. Something must be done about it." He's considering bringing in their "associate." Ooh! They have an "associate!"
Somewhere! A jerk on a cellphone tells someone that he returned the money so he wouldn't get arrowed. Then he gets black-arrowed in the back. Once the police are there, we learn that he was Nelson Ravitch, who was targeted earlier by the hood. The commissioner says that if they announce that there's a hood copycat, then it will be a serial killer case, which will cause panic. Well, that doesn't hold up, given that Helena killed multiple people. And so did China White. And Deadshot. And Oliver, for that matter. So you'd think the local news wouldn't get excited at someone who killed only two people. The commissioner tells Detective Lance to catch at least one of these psychos. Lance says he won't blame the regular hood for this murder, and the commissioner overreacts: "You're off this case, sergeant. Effective immediately." So now he's been demoted from Detective Lance. That sort of thing happens pretty suddenly in television shows and movies, but I imagine that in the real world, even the police commissioner needs to fill out some paperwork to demote someone. And shouldn't he assign someone new to the hood investigation?
Obviously, Detective-now-Sergeant Lance picks up the secret phone and makes a call. Oliver picks up and immediately warns him, "Don't trying to trace this back to me. You'll never make it through the encryption." He can encrypt cellphone calls beyond the ability of the police to trace it because of Island Knowledge. Lance tells him where he'll find his arrow. Oliver warns him about setting a trap, and Lance tells him he has until Christmas. "And then, copycat or not, I'm coming after you." You're supposed to have been coming after him for the past nine episodes!
Oliver studies the arrowhead from the black arrow, which is all serrated. He tells Diggle that it's a teflon-coated titanium blade, serrated to split the bone. And the shaft is some kind of specialized polymer, stronger than typical carbon fiber. Sooo... I guess he learned metallurgy and some degree of chemistry on the island. Sure. Fine. So he decides that these arrows were custom-made. Diggle wonders if the guy's trying to frame Oliver or call him out. If he's trying to frame Oliver, you'd think he'd use the same kind of arrow. Also, there's no real need to frame him, since he's running around breaking the law on his own.