The Halloween episode of Community last year was very good, but it also came before the moment in the series' run (around "Contemporary American Poultry") that the show began to evolve into something infinitely more entertaining and rule-breaking than a typical sitcom. As a result, last night's holiday-themed "Epidemiology" was far more inventive and gripping, turning a Halloween party into a hypertextual riff on zombie flicks and genre thrills. But as always, the creators ground the increasingly surreal antics in a very real world, both in terms of making the events canonical and in giving the viewer a legitimate human-interest story that parallels the surrounding craziness. Everyone turned into a zombie last night, but only as a way to show that Troy wasn't quite sure what kind of person to be. (Or, more literally, if he wanted to use his brain or become a mere body.) I was also impressed at the way the episode -- credited to writer Karey Dornetto and directed by Anthony Hemingway -- rationalized the zombie threat into a real, if far-fetched, sickness. Smart, entertaining, and just plain wonderful TV.

The actual mechanics of how everyone turned into zombies were handled swiftly, as if to acknowledge that such details are kind of beside the point. The dean's food supply for the Halloween party was bought from an Army surplus store and turned out to be toxic waste product that, to quote the suddenly returned Dr. Rich, carried a "rabies-related pathogen affecting the prefrontal cortex of the brain causing hyper aggression." Yada yada yada, everyone's quarantined for six hours until the Army can show up and fix things, leaving the study group to band together and fight for survival.

But even before the party got out of hand, Troy was bristling at being labeled a nerd when he failed to get a girl's phone number after showing up in Aliens-inspired group costume with Abed, starring Troy as Ripley in a power loader and Abed as an alien. The brilliant thing about Community is that the further it strays into wackiness and irreverence, the tighter its grip becomes on its main characters and what it means to care about them. Without Troy's very understandable and relatable identity crisis, the rest of the episode would be just a cute gimmick; with it, it's fully rounded.

This is a horror movie homage, though, which means a much higher body count than in something like "Modern Warfare." Pierce was infected before the credits and started biting people right away, and the crowd eventually took down Britta and Annie before the rest of the group was splintered. It was surprising at first to see the big guns like Jeff get taken down, but then, this one had to be about Troy, who continued to fight to get to the thermostat so he could cool down the building and break everyone's fever. (Again, sitcom zombies.) He got his dumb-but-energetic moments, his panic moments --screaming "YOU PUNCHED A LADY BEE" when Jeff slugged a zombie was hilarious, and reminiscent of this -- and his heroic moments, as he made up with Abed and saved the day. An adventure story, horror movie, and buddy comedy all in one, narrated by George Takei. What better treat could you want for Halloween?

Scattered thoughts:

• Too many geek references to name, but my favorite was probably Troy and Abed's nod to The Empire Strikes Back with "I love you"/"I know." Great reference, and a nice moment for the guys to come back together.

• A great Abed meta moment came when he saw the zombie crowd approaching and said, "I hate to be the 'We've got company' guy, but...." That line is used more than you think.

• The themed credits were a cute touch, and enough to make me wonder if creator Dan Harmon will do that for all holiday eps from now on, or at least Halloween. This could be the new "Treehouse of Horror."

• "Make me proud. Be the first black man to get to the end."

• Throwing Chang and Shirley together was so insane it was perfect. No idea if Chang's voicemail to Troy will have a lasting effect, since the Army knocked everyone out MIB style and told them they'd all been roofied, but it'd be great if it did.

(Clip from last season's "Contemporary American Poultry")