In last night's Supernatural, called "Swap Meat," Sam and Dean arrive in a small Massachusetts town to fight a poltergeist - but wind up tangling with something much more dangerous. An MIT-bound nerd who loves Latin.

Like many of the best Supernatural episodes, this one started goofy, and wound up taking us to a really dark place peopled by unexpected monsters. The brothers are on a relatively cut-and-dried mission to exterminate a poltergeist who is tormenting the daughter of their old babysitter. (She makes an offhand comment about how once she had to babysit them for two weeks while their father was out hunting, just a throwaway line but packed with sadness.)

Quickly, however, their routine mission gets thrown off-course when a 17-year-old Satanist named Gary spots them in the fast food restaurant where he works and decides to swap bodies with Sam. See, Gary is fed up with the way his father is always pushing him to stay on "the plan," which is to do everything humanly possible to get into MIT and become an engineer. Asthmatic, passive, and dorky (though also sort of hot), Gary has turned to an ancient Satanic book for answers. When he and his buddies finally raise a demon, it transmits a psychic fax from Lucifer, which is a "most wanted" poster featuring Dean. So when Gary sees Sam and Dean, he decides to hand them over to the demons - and ask for the "reward" of being made into "a real witch."

Before we delve the funny/tragic elements of the life of a teen geek Satanist, I just want to pause and point out that I love the idea that Lucifer is sending out "most wanted" posters via seance. Basically Gary is possessed briefly, draws a picture of Dean, and transmits the message that this guy is "hell's most wanted." Demonic messaging is better than an email blast!

The meat of the episode focuses on what happens after Gary executes his non-brilliant plan for handing the brothers over to the demons. He'll possess Sam's body, kill Dean, then hand over Sam's much-desired meatsack to the demons. But it turns out that what Gary really wants is to be an independent adult. Or at least, a teenager's idea of an independent adult. There's a winceworthy scene where Gary-inside-Sam checks out his muscles in the mirror. Then he spends the evening drinking, eating burgers, and having sex - all while Dean grows more and more suspicious of this very unSam behavior.

Meanwhile, Sam is stuck in Gary's body (and his unenviable wardrobe) and delivers some amusing bitchslaps to Gary's controlling father while trying to figure out what the hell is going on. As you can see in the clip, this dad smackdown scene is seriously bizarre. I love that we're in the middle of a scary Lucifer-related scenario, but there's still time for Sam to help Gary in his quest to escape his father's smothering expectations.

There's also a tip of the hat to Supernatural's running gag about how Dean secretly wishes Sam were a little more badass. In some ways, Dean has a lot more fun with Gary than he does with Sam - they bond over burgers, booze, babes, and rock in a way that the real Winchester brothers never will.

By the time Gary half-heartedly tries to shoot Dean, our intrepid Winchester has already figured out the body-switch. Gary is regretting what he's done, anyway, especially after all that bonding with Dean and getting laid. Dean and Gary race to the rumpus room where Gary's pals have Sam-inside-Gary tied up, and have raised a demon who is ready to claim the brothers. Luckily, Gary is really good with Latin and knows the spell for exorcism.

The whole episode is about to end on an After School Special note, with the brothers delivering Gary (in his own meatsack, thank you) to his house, giving him a pep talk about sticking up for himself ("in a non-Satanic way") and how they "wish they had his life." But then, Supernatural style, it's all turned on its head. After Gary is out of earshot, Sam mutters to Dean, "Actually his life sucked."

Next week promises to be a major dustup, with Anna the rebel angel traveling back in time to prevent Sam and Dean from being born. Yay for arc episodes!