Nathan Dean

A group of teenagers are driving on the freeway when a skull smashes through their windshield. At the Jeffersonian lab, Brennan tests out a young forensic anthropologist to replace Zack, who has left for Iraq, and she and Cam examine the skull in question. They find it has marks made by human teeth, suggesting cannibalism. The team identifies the victim, a known violin protégé who disappeared after a concert. On a quest to find out what happened to him, Brennan and Booth go into the field. A trail of suspects leads them to a strange cannibalistic society, and the team must string together a gruesome and cryptic series of crimes - provided that Brennan and Booth can survive the newfound tension between them. Meanwhile, Cam suggests that Angela hire a private investigator to track down her ex-husband so she can annul her previous marriage and marry Hodgins, a task easier said than done.

After Booth has a bedroom romp with his ex-girlfriend Rebecca, he gets a call from Brennan about their latest case and agrees to meet her at a condominium construction site. They're led into a partially built unit where they find the gruesome remains of a man dissolving in a bathtub of household cleaning products. After determining the victim had Brittle Bone Disease, they search a database of area BBD victims, all of whom are children, and split up to visit them in hopes of finding a connection to the dead man. When both Brennan and Booth come back with confirmation of the man's identity, they realize he was living a double life with two different families. In what first appears to be a straightforward case of jealousy and insurance money, new clues send Brennan and Booth in a completely different direction and a third suspect is brought to light.

After construction workers find the body of an archbishop whose kneecaps were surgically removed, the team is back on the case of the Widow's Son serial killer. When Angela discovers what appears to be a victim tree in the evidence vault, the team realizes the killer employs a systematic pattern in selecting victims. With a musician and an archbishop the first to go, the team tries to predict who might be next and how they can stop the killer before he strikes again. Brennan and Booth continue to see Dr. Lance Sweets (John Francis Daley), who has some helpful psychological insights into the Widow's Son's motives. Meanwhile, Brennan's brother, Russ, comes out of hiding when he finds out that his girlfriend's daughter is extremely sick, but his appearance causes Booth to intervene with Brennan's family once again.

When a terrified young Halloween reveler finds the mummified remains of a teenage girl in a Halloween pumpkin patch maze, Brennan and Booth are called to the scene to investigate. They are perplexed by the fact that the girl appears to have been deceased for at least a year, while Hodgins discovers her body is covered with spider bites. Booth and Brennan later receive word of a second mummy found at Halloween amusement park funhouse, and it appears the victim, another teenage girl, was killed on Halloween approximately two years prior. As the team questions a variety of ghoulish amusement park employees, from the grim reaper to a zombie, they get word of a third teenage girl who has gone missing. Booth and Brennan realize that they have until Halloween to find her before the killer strikes again. Meanwhile, the team gets decked out in costume for the annual Jeffersonian Halloween Ball, and they encounter a few scares of their own.

Brennan, Booth and the Jeffersonian team are called in by the Bancroft family, major donors to the Jeffersonian, to investigate the death of Terence Bancroft, who was found dead at home, bound to his desk chair and maliciously stabbed. The team proves the body had been there for almost a month. Booth questions Terence's wife, Clarissa, while the team brings the body and all the evidence back to the Jeffersonian for further tests. Hodgins removes an old photo of himself with the victim from official evidence so the others won't see it, knowing the photo links him to the case. When the case goes to trial and Hodgins' involvement is revealed, the Jeffersonian's reputation is jeopardized, prompting Brennan to make an important decision about her team. Psychiatrist Dr. Gordon Wyatt has cleared Booth to carry a gun and go back to work, but it's contingent on Booth continuing to meet with Wyatt on a few underlying issues - issues that may be creeping into Booth's judgment and affecting his investigative work. Meanwhile, Agent Sullivan invites Brennan to one of his basketball games and the heat is turned up on their relationship.