An unseen man with a sword slices the hand off of a man attempting rape in an alley. After cutting off the man's hand, he swings again and cuts the man in two. The man who was killed is Tyler Faris, an ex-convict who was recently involved in an altercation with a member of the mob – Tony "The Butcher" Valtini. He believes that Tyler Faris was attacked and killed by the same man that had attacked him with a sword. The only images the security tapes can find of the killer is a man wearing a red costume with a mask. Castle is stocked that the killer is a superhero and dubs him the Red Maroon.
Beckett watches the security footage of the Red Maroon and she and Castle head to the comic book store, Comicadia, to learn more about real-life crusaders. When they arrive at the store, the owner recognizes Castle and shows him that they sell Castle's graphic novel, Deadly Storm. Most importantly, the owner is able to recognize the Red Maroon's costume. It is exactly like a superhero outfit worn a comic called "Sword of Lone Vengeance." They learn that the character was created by Sean Elt. They also find out that there's a knuckle plate as part of the costume and Castle recalls seeing it at the scene of the crime but the Lone Vengeance had taken the plate and made a clean exit. However, Exposito knows the secret identity of this superhero.
Beckett arrests a man who was dressed as Lone Vengeance – his name is Chad Hockney. Chad, however, has an alibi. He says that the man they're looking for is actually still out on the streets. Castle realizes that the real Lone Vengeance has been reenacting all the crimes that were depicted in the comic and he believes that the real Lone Vengeance is actually the creator of the character, Sean Elt. The writer's name is actually an anagram of Stan Lee's name – one of the greatest comic book writers.
They learn that Tyler Faris was a big fan of Lone Vengeance and that he also knew one of the reporters at the crime scene – Paul Whittaker (whose real identity is Sean Elt). Whittaker is a former graphic artist. Tyler Faris was the source who had tipped the reporters about the Lone Vengeance crimes and had figured out that Whittaker was the real identity behind the mask. One theory is that Faris had figured out Vengeance's identity and had threatened to expose him.
Paul admits to being Lone Vengeance and is ready to confess to killing Faris but Castle and Beckett realize that he is lying and actually protecting the actual Lone Vengeance. The duo finds the hero's hidden lair and wait for his return. When Lone Vengeance removes their mask, Beckett is shocked to see that it is actually Ann Hastings, one of the police officers who was at the scene of the crime. She says that she didn't kill Tyler but she stole the knuckle plate to help her figure out who did it. Castle and Beckett believe that the killer wanted Faris dead and to frame Lone Vengeance because his vigilante ways were hurting illegal street businesses. The finger prints on the knuckle plate confirm that Tony "The Butcher" was indeed the killer.
At home, Castle is still having problems coming to terms that Alexis is going to Stanford in a few short months. He's still afraid she's going because she is following Ashley's dreams rather than her own.