In a standard mob sting (where the trained police have to be bailed out by Oliver and Sara, because putting on a mask makes you great at fighting), Frank Bertinelli gets picked up. This worries everyone, because it means his daughter Helena is going to come to town and try to kill him. Sara takes the news that Oliver has an ex-girlfriend who's a murderous vigilante surprisingly well. She points out that he clearly has a type, which would be a better joke if it didn't require us to forget about Laurel. So the team has to go out on the road to stop Helena's expected attack. They're attacking a decoy, so the only thing that's accomplished is that Roy gets shot through the hand and he gets consumed by Mirakuru rage. Oliver distracts him by reminding him of Thea, but Roy thinks Oliver is calling him "Speedy," which is one of Roy Harper's superhero names in the comic books. It's cute! Unfortunately, it doesn't stop Helena at all.
Laurel is working on her recovery by going to two meetings a day, when she receives an unexpected offer. Her old boss Adam invites her to come back to the District Attorney's office and run the prosecution of Frank Bertinelli, because she's an expert at RICO law. Sara and Oliver aren't sure she's ready to go back to work, because she might have a relapse. Although it turns out that the real danger is that she might be in the court house when Helena tries to murder her father, because then it might be a police trap that goes wrong. And after all of those things happen, Helena ends up taking a lot of hostages and telling the police that she'll start killing them if they don't hand over her father so she can murder him as revenge for her fiancé. And Laurel has to hide in the building, like she's John McClane or something.
Sara has to break in and rescue her, because Oliver is caught out in the open where he can't change into the Arrow right away. But when Sara gets Laurel into a safe room, Laurel wants to start drinking immediately. Sara delivers an impassioned speech that works so well that not only does Laurel not drink, but she also refuses to be rescued without the rest of the hostages. So Sara has to go fight Helena and get knocked out a window. Helena has a new offer for Oliver: she'll trade Laurel for Frank Bertinelli. Quentin's willing to help out on that, because he puts his daughter's safety above the law.
The handoff takes place at the corner of Gail Street and Simone, which is a great reference. It doesn't go very well, because the police get there, too, and they don't mind shooting at vigilantes like Helena, Sara or even Oliver. Sara and Helena have time to have another fight, and Sara does better in this one. She doesn't kill Helena, and Helena is very sad to learn that her father was killed in the crossfire. She wanted to murder him herself! But you can't always get what you want, as Sara learns in the flashback storyline, where she decides to turn Hendrik the Jerk over to Slade in return for Oliver, who spends the whole flashback shirtless and being electrocuted.
In the end, Roy breaks up with Thea because he doesn't trust himself not to fly into a Mirakuru rage around her. And Laurel manages to keep her new job by blackmailing the District Attorney. Helena goes off to jail, but she'll probably be back. And Thea gets a ride home from Slade Wilson, just to remind us that he still exists.