A man's hand is sliced off during an attempted rape in a dark alley. The unseen sword-wielding assailant swings down mightily to sever his prey straight down the center, splitting him in two. Can't you just hear Castle saying something like, "This guy's half the man he used to be?"
The dead man is an ex-con named Tyler Faris. He recently got into an altercation with mob man Tony "The Butcher" Valtini, who says Faris was likely killed by the same vigilante who attacked him with a sword. Tony shows the L-shaped scar that was left on his butt cheek. Surveillance footage shows the attacker wearing a slick red costume and mask. Castle is positively giddy. He exclaims, "Our killer is a superhero!"
Castle shows Beckett video footage of the Red Maroon, a wannabe superhero who is proof that subculture of real-life crusaders exists. They check out the one place any true collector of comic books is sure to frequent: Comicadia. The store even sells Castle's Deadly Storm graphic novel. More importantly, the shop owner recognizes the costume the killer wore. It matches the one seen in a comic titled "Sword of Lone Vengeance."
The Lone Vengeance character was created by a guy named Sean Elt. The comic hero's suit features a knuckle-plate that Castle remembers seeing at the crime scene. Sure enough, the evidence is on the ground in the alley. Too bad Lone Vengeance swoops in to snag the knuckle-plate while making a clean getaway. Fortunately, Esposito now knows this particular superhero's secret identity.
Beckett arrests Chad Hockney, a guy who dresses like Lone Vengeance. This wannabe hero, formerly known as Red Maroon, has an alibi. He says the real Lone Vengeance is still out there. Castle realizes that the comics emulate the events of crime scenes, such as the L on Tony the Butcher's derriere. He believes the killer is the writer of the Lone Vengeance stories: Sean Elt.
Sean Elt is not a real person. The name is actually an anagram of Stan Lee-the king of all comics. The team learns that the victim was really into Lone Vengeance. Tyler Faris also knew a reporter Beckett and Castle saw at the crime scene. His name is Paul Whittaker (aka Sean Elt), a former graphic artist. Tyler Faris was a source who tipped off Whittaker for his crime beat. The theory is that Faris figured out Whittaker was Lone Vengeance and threatened to expose him. Of course, that's just a theory.
Paul Whittaker says that he's Lone Vengeance and is prepared to confess to killing Tyler Faris. But Beckett and Castle realize he's covering for the real Lone Vengeance. They find the secret lair of the superhero in question. When Lone Vengeance returns, Beckett and Castle are waiting for him. When the mystery vigilante is unmasked, Beckett is stunned to see it's a police officer who was at the crime scene: Ann Hastings.
Officer Hastings swears she didn't kill Tyler Faris, though she did swipe the knuckle-plate in order to figure out who did. Someone else dressed as Lone Vengeance must have chopped down their dead guy. Beckett and Castle believe the killer wanted Tyler Faris dead, but also wanted to frame Lone Vengeance, who just happened to be hurting the illegal street business of Tony "The Butcher" Valtini. Fingerprints on the knuckle-plate prove that this guy's the killer. Case closed.
Ann Hastings the cop and Paul Whittaker the writer seem to have a similar relationship to our favorite homicide detective and her mystery novelist partner. Beckett has some words of wisdom for Hastings. She says, "You're a good cop and you've got somebody who cares about you. Don't be so driven by the past that you throw away the future." That's good advice.
In other news, Castle is still having trouble with the fact that Alexis is heading off to Stanford in January. He worries that she may be following Ashley's dreams instead of her own. This leads to a somewhat heated discussion, but Alexis eventually realizes her dad is right. She'll focus on following her own passion at Stanford. Unfortunately, that may include moving in with Ashley.