A group of geeks dressed up like wizards, warlocks and an elf walk through a sewer tunnel. Little do these geeks know the sewer is a great place to find a dead body. Sure enough, the geeks run screaming at the sight of a rotted corpse, which appears to be as dressed up as they are.
Brennan visits Booth's apartment. The latter asks the former to fix his sore back. "You need a medical doctor," Brennan insists. Turns out the poor agent has a herniated disc and will be on bed rest for the remainder of the week. Enter Agent Perrotta, who will be assisting Brennan. Neither seems particularly happy about it. Time to examine the body. Brennan notes the vic has severe facial damage. Perotta discovers a strange stamp on one rotted hand. From a bar, perhaps? Not even close. Intern Fisher recognizes the stamp as coming from ImagiCon, a geek gathering in town for the weekend. Angela goes to the convention Web Site and finds a photo of a woman in the victim's geeky costume.
Brennan and Perrota head to ImagiCon, where they are shocked to find all levels of geekery on display. "I'm at loss for the anthropological analog," Brennan says. Who's the geek now? Anyway, the pair interview one of the other convention models, who says the victim talked of "sitting on a goldmine." But what goldmine? A medieval geek at a nearby booth, Peter Kroon, quickly unravels the mystery. Turns out Kendra, the victim, had an Excalibur sword from the famous movie Le Morte d Arthur. "The prop was worth tens of thousands," Kroon explains. "That sword hasn't been seen in 20 years."
Back at the lab, Brennan gives Booth a call. He practically begs for a massage but Brennan isn't biting (or rubbing, as it were). Then Perrota calls Booth to see if the agent needs anything. Brennan and Perrota enter Kendra's condo to find it ransacked. "Looks like someone really wanted that sword," Brennan says. Back at the lab, Hodgins has discovered blood found on Kendra's princess boots matches a rare toad residing in nearby park. Also: dirt under her fingernails indicates she did some digging. "She went for a run, stepped on a frog and buried something," Camille says.
Perrota, in the meantime, has found an angry message on Kendra's voice mail. She plays it for Sweets. "You've got three days," the female voice says. "I want that sword." The pair head to ImagiCon to interview the man who appraised the sword for the upcoming convention auction. Sweets plays the voice mail for the man, who identifies the voice as belonging to Valerie Daniels, a "medieval weapons collector."
Goth queen Valerie is brought in for questioning. "I like sharp edges," the woman coos. "I like sharp against soft." Sweets swallows hard. Valerie then explains Kendra claimed to have been given the sword "as a gift" by a man dressed as a Black Knight. "I didn't kill the girl," she says. "I just wanted the sword." Hodgins and Angela, meanwhile, are combing the park with metal detectors for the sword. Before you can say "I am the once and future king," the detectors start beeping like crazy. Hodgins finds the sword buried just beneath the surface.
Back at the lab, Sweets and Hodgins have hatched a plan. They will return the sword to ImagiCon and put it up for auction. Sweets will act as a buyer and purchase the sword in a fixed auction. "I'm confident that if our killer is there, this will provoke him to reveal himself," Sweets says. It's just crazy enough to work.
Cut to the auction, where Sweet sits in the audience wearing a red Star Trek shirt (bad mojo). Brennan and Perrota watch the crowd via a hidden camera. The former notices a Black Knight standing motionless in the corner. Valerie immediately bids $50,000. Sweets counters with $60,000 and the bidding quickly goes up. A man in a suit soon bids $400,000. Sweets counters with $500,000. "Sold!" yells the auctioneer.
As the crowd clears, Perrota confronts the well-dressed man with the British accent. "I represent a group of collectors," he explains. "They wanted the sword." But how badly? We cut to Sweets and Brennan driving home from the auction when -- BANG! A car slams into the driver's side door! None other than the Black Knight emerges from the attacking sedan. This doesn't sit well with Brennan, who stumbles from the wreck and begins fighting with the Knight -- with Excalibur! Booth would be proud. Eventually, Brennan gets the best of the Knight, who flees. "Mad props," a bloodied Sweets mutters before passing out.
Back at the lab, Brennan and Sweets are fine. Hodgins runs tests on paint chips left behind by the Black Knight's car. "Paint is from an early 90s Ford Explorer," Hodgins says. Camille, meanwhile, finds the Black Knights blood on the sword (way to go Brennan!). Intern Fisher enters with news: the murder weapon was a "medieval torture device" called the "Pear of Anguish." The device was inserted into the victim's mouth and then slowly opened, crushing the orifice outward. Gross. Brennan takes the opportunity to relive her battle with the Knight. "I was attacked well-trained in archaic martial arts wearing chainmail," she says. Brennan and Hodgins head to the scene of the car accident with the metal detectors. They soon find a piece of chainmail.
Back at the lab, Fisher has tracked the chain mail to a man named Peter Kroon. Remember him? Seconds later, Kroon is being interrogated by Perrota and Brennan. "Your car shows that you are the person who drove Dr. Brennan and Dr. Sweets off the road," Perrota says. "Your wound matches the one Dr. Brennan delivered to her assailant. It was your blood on the sword. And we found fragments of your chainmail."
The only question is: Why?
"I loved her," Kroon explains. He gave Kendra the sword out of love and she turned around and tried to sell it for rent. Then, Kroon killed her for the offense. Brennan is baffled. He killed Kendra over a movie prop? "You don't understand," Kroon says. "No one understands true love anymore."