'Bones' season 12 episode 9 spoilers: Team goes undercover in demolition derby competition; Brennan continues to deal with losing her father

The team goes undercover to investigate a hay baler accident on the upcoming episode of Fox's procedural drama "Bones" season 12.

Titled "The Final Chapter: The Steel in the Wheels," next week's episode will center on a tragic death involving a hay baler machine. According to the official synopsis, a young man dies in a tragic hay baler accident. To gather more pieces of evidence related to the case, Brennan (Emily Deschanel), Aubrey (John Boyd), and Booth (David Boreanaz) must wear trashy disguises and go undercover. The trio head to a rowdy demolition derby competition where they find new leads about a possible suspect.

Meanwhile, a fan-favorite character will come back to help on another case.The ongoing Gormogon case suddenly hits a dead end, so Dr. Gordon Wyatt (guest star Stephen Fry) steps in to help Hodgins (TJ Thyne) and Cam (Tamara Taylor).

Tuesday's episode also featured the return of a person from Brennan's past: Sully (guest star Eddie McClintock). The hour saw Brennan struggling to open up to Booth about her grief after her father died. It came to a point where she even asked him to let her spend some time alone. When Booth goes out of town to work on a case, Sully resurfaces out of the blue and tries to comfort his ex. The episode wrapped up with Brennan finally connecting with Booth.

Co-showrunner Michael Peterson recently spoke with TV Line, and he shared how Brennan will continue to deal with her father's death. "In the next episode, she's still reeling from the death of her father," he said. "Her journey to figure out what happened to her parents; that's the central arc when you meet Brennan in the pilot. It's about her discovering family. To find her father and to go through this journey with him, to finally forgive him for all that has happened, and then to lose him, it's a defining moment for them. This crucible... it's going to continue to the end of the season," he added.

The 12th and final season of "Bones" airs every Tuesday night at 9 p.m. ET on Fox.