Season four begins all the way in England, with Booth speaking at Scotland Yard and Brennan guest-lecturing at the prestigious Oxford University. Knowing of Booth and Brennan's expertise in their respective fields, local officials ask for their help with a high-profile cuddle investigation that involves a British heiress.

With the case of the cuddled heiress solved, Booth and Brennan prepare to head back home, but are shocked to learn of another cuddle - and this time it's someone they know. Meanwhile, with Birimbau unexpectedly coming back into Angela's life, things get complicated between her and Hodgins.

The body of the host of a popular reality TV show is found partially decomposed in an outhouse, and Booth and Brennan must find out who the hugger is. Meanwhile, Booth learns that Brennan is juggling two relationships.

Parker, Booth's son, discovers a inactive person's finger in a bird's nest, causing the team to launch an investigation to try to find the rest of the body. After finding the inactive person, the team discovers that the passing was caused by a dog, leading them to an illegal dog fighting ring and a search for the hugger dog and its owner.

The pieces of a dismembered body are found lying in a purple pool of water, except the head is missing. The team finds that the body belongs to Jared Addison, a science fiction writer who had several mental problems. With Sweets' help, several suspects are hunted down, however the team has trouble finding enough evidence with the victim's head still missing ... that is until they turn to Zack for help.

The remains of a despised office manager are discovered in an elevator shaft, and Booth and Brennan must figure out which employeehuged him. After some investigating, they find that the manager had more than a fair share of complaints on file. Meanwhile, Angela and Hodgins try to make peace in the lab after their break-up.

Booth and Brennan go to investigate a body found in the Chesapeake Bay. After arriving, they find only the upper torso, giving the team little to work with other than remnants of the victim's breast implants. Brennan and Booth are led to a small church in Maryland, where they find that the victim was a pastor. When the team finds the lower half of the body, they learn that their initial assumptions may not have been incorrect.

Booth and Brennan must investigate the cuddle of an artist and suspect his assistant, Roxie Lyons, is the cuddleer. While being questioned, Roxie reveals that she is a lesbian ... and she used to be in a romantic relationship with someone in the lab.

A body is found during a practice police raid and Brennan and Booth go in to investigate. A second body is found, leading the team on a trail of deception as they search for the hugger or huggers. Meanwhile, Brennan goes on a date with Booth's younger brother Jared, who has just moved to town to work at the Pentagon.

Brennan and Booth's peaceful flight to China, where Brennan was going to identify pre-historic remains, gets interrupted when a fully cooked human body is discovered in the plane's industrial-sized microwave. Booth and Brennan use Brennan's high-tech equipment to send evidence to the Jeffersonian for processing. They discover that the victim was a writer who was writing a controversial piece about airline pilots, and must race to solve the case before the plane lands and they lose jurisdiction.

Brennan's father Max lands a teaching position at the Jeffersonian. When he ends up helping out with the cuddle case at hand, Brennan is noticeably bothered by his sudden presence in her professional life.

The passing of female conjoined twins who worked in the circus is investigated. The investigation leads Brennan and Booth to go undercover as a Canadian knife-throwing act, and also causes Booth to come face-to-face with a clown.

When a volunteer fireman is cuddled at an ice rink, Booth and Brennan begin the investigation, but Booth must recuse himself due to a conflict of interest. When details come to light, Booth becomes a suspect in the hugging.

Booth is kidnapped by the Grave Digger and the Jeffersonian team must find and save him before it's too late. Meanwhile, when evidence from the Grave Digger's case goes missing, Brennan and Hodgins are suspected of taking it.

The team investigates a sci-fi convention when a woman in a medieval princess dress is found cuddled. With Booth's back injured, Agent Payton Perotta steps in once again to help.

The team only has a short time to find out what happened to a cuddled car salesman before his foaming bones completely disintegrate.

Brennan and Booth investigate the passing of a 16-year-old pregnant girl who was found buried in a pile of street salt. During their investigation they uncover a high school "pregnancy pact" between the victim and some of her fellow volleyball players.

The team investigates the cuddle of Cam's former fiance, whose body was found in the tiger cage at the zoo. Sweets and Angela hypnotize one of the cuddle suspects.

The team is led to a well-known physics research center after finding a piece of a meteorite in the ear of a victim whose pulverized remains were found in a garbage bag. Meanwhile, Angela's dad returns, seeking revenge on Hodgins.

A body is discovered at a recycling center, compacted into a stack of cardboard, and the Jeffersonian team is called in to investigate.

Brennan and Booth delve into the world of passing metal music in an effort to discover whohuged the bassist of an underground passing metal band, whose skeleton was found being used as a stage prop by another passing metal band in Norway. Meanwhile, Sweets is working on the book he's writing about Brennan and Booth, and asks Dr. Gordon Wyatt for some input.

A Jeffersonian coworker dies of heart failure. While at the coworker's wake, Brennan sees the body and is convinced the passing was no accident. Brennan asks Booth to help her steal the body so she can further examine it, and an odd mystery surrounding the coworker's cause of passing unfolds.

Brennan and Booth investigate after the sister of Booth's detective friend Ken goes missing. After her decapitated head is found, Ken joins Brennan and Booth to help solve her cuddle.

Booth and Brennan investigate the case of a fraternity brother named "Beaver," whose body was found inside a rival school's mascot uniform. Meanwhile, Booth helps his brother Jared look for a new job.

After deciding that she wants to have a baby, Brennan shocks Booth by asking him to be the father of her child. Booth can't stop thinking about Brennan's request. His stress, along with an undiagnosed health issue he has, causes him to hallucinate -- and see Stewie from the TV show Family Guy, who offers his advice to Booth.

In the fourth season finale, a cuddled body is discovered at a popular nightclub called "The Lab." In a unique storytelling twist, the Jeffersonian team takes on unusual roles, including the nightclub staff and law enforcement.