This weekend will mark the second time that an advance wave of invaders from planet geek descends on the Javits Center. Wearing Wolverine t-shirts and black leather trench coats, armed with mint-condition comic books and an encyclopedic knowledge of fictional universes, these are the guests at the second New York Comic Con (February 23–25). Last year organizers expected 10,000 attendees and were buried beneath an avalanche of 33,000. Lines lasted for hours, and the police showed up to keep things moving. The convention has doubled in size this year, and tickets have almost completely sold out.

Video games and movies are being launched at the Con and the guests of honor include Stephen Colbert, Stephen King, and Wes Craven, but comic books are the main event, specifically superhero comics published by Marvel (weighing in with 44% of the marketplace) and DC (weighing in with 34%). How do two companies control such an enormous slice of the pie? By bumming everyone out. In recent years, Spider-Man has killed Mary Jane with his carcinogenic spidersperm. Batman has become a single parent. Captain America and Iron Man are hashing out national security issues by hitting each other in the face while rounding up unregistered superheroes and sending them to a Gitmo-style prison camp after a superpowered September 11, 2001. The once cheerful Elongated Man saw his wife raped, then burned to death. And the new Batgirl is an evil, lesbian junkie. No wonder Superman has spent the past year with his forehead buried in his hands, weeping softly.

“It’s dark out there,” said Dan Buckley, publisher of Marvel comics. “But the stories go where the stories go.” And fans want them to go somewhere full of grim and gritty relevance while still wrapped in comfortable nostalgia. “Books that lean more toward the humorous don’t do as well in the hobby market,” Mr. Buckley said. “It doesn’t mean we don’t want to produce those books, but we have to sell to our readership.”

The sales of comics have declined steadily since their heyday in the 1940s — the average comic book now sells around 20,000 copies. Comics fans are largely a graying crowd, with younger readers gobbling up manga, Japanese comic books that sell in huge numbers, while ignoring superhero comics that sell in specialty shops.

“It’s a common idea that the superhero market is getting older and isn’t replacing itself, but that’s not entirely true,” a comics journalist for Publisher’s Weekly, Heidi MacDonald, said. “There are young men and women getting into superheroes, but they’re not coming in vast numbers.”

By basing their books on world events, the comics industry has recently driven up readership among the faithful, a trend that hit its peak this Wednesday with the conclusion of Marvel’s “Civil War.” Spanning seven months and approximately 124 different issues, this series used superheroes to make a sweeping and awkward metaphor about post-September 11 civil rights. The core miniseries sold around 200,000 copies per issue, and tie-in titles got a sales bump of about 20,000 copies per issue.

“They were mostly an influx of lapsed readers from the 1990s,” said Mr. Buckley. “Although we did get some new readers from the mainstream press we received.” DC Comics, home of Batman, Superman, and Wonder Woman, has also made use of current events for their comics. With names like “Infinite Crisis,” “Identity Crisis,” “Secret Wars,” “Civil Wars,” “World War Hulk,” and “World War III” their comic series have become an inaccessible haze of wars and crises only a true believer can follow.

In order to shoehorn 70 years of comics into one universe, DC Comics has had to invent over 30 different Earths, causing so much confusion that they eventually destroyed them all in the 1980s (“Crisis on Infinite Earths”) and then recreated them all in 2005’s “Infinite Crisis,” which ended with Superboy punching reality so hard it broke. Fans love this kind of insular, self-referential story partly because familiarity with these details is what separates insiders from outsiders and insiders have their privileges. Comic book writers join the staff of the television show “Lost,” and writers from “Lost” plot comic books. Joss Whedon, creator of TV’s “Buffy the Vampire Slayer,” has become one of the hottest writers in comics. Comic books have become the secret handshake that gets you in the door of the pop culture boys club, the bona fides that establish your hardcore geek-chic credentials.

Like pilgrims who walk hundreds of miles on their knees, the surest sign of true devotion to comics is to immerse yourself so deeply in them that they exhaust you. At New York Comic Con, fans will stretch their brains with mountains of trivia and strain their backs with swag. The line between fan and creator is very thin. “I don’t think you’ll see anything quite like ‘Civil War’ out of us again,” Mr. Buckley said. “It’s exhausting for the editors. It’s been great, but it’s exhausting.”