Tom Billett

When the unearthed remains of Mason Roberts, a federal prosecutor who disappeared five years earlier, are discovered in the desert outside Las Vegas, Brennan and Booth suspect his death may be tied to the mob. The body count in the desert rises when vultures lead them to the recent remains of a young woman, just a few yards away. Booth suspects the same person may have been responsible for both deaths, but the woman's injuries lead Brennan to believe she has a long history of domestic abuse and her husband may have been responsible for her demise. Brennan and Booth question the deceased woman's husband, who denies he hurt his wife, but leads them to a Vegas loan shark. When an anonymous lead takes them into the world of gambling and underground ultimate-fighting, Booth and Brennan go undercover as Vegas high-rollers. Booth takes his turn in the ring and risks his life in a desperate effort to undercover the mystery.

When Dr. Alicia Seberg, a government research scientist (guest star Amy Price-Francis), is exposed to a deadly toxin while at work and has only hours to live, she calls Patrick Jane and the CBI to find her murderer.

The CBI team is faced with a violent and shocking crime in its own office, but must work the case in spite of their alarm of who may be behind it. Meanwhile, Agents Rigsby and Van Pelt are definitely an "item".

Ducky is attacked by a man who claims to have information about his half-brother, who died decades earlier; Jake and Bishop talk about their future.

Killers target the Boston homicide headquarters, trapping Jane, Maura and Frankie Jr. in a fight for their survival.

A secret investigation conducted by Beckett related to her mother's murder goes awry when a man she has been surveilling is killed. When evidence links Beckett to the victim, she and Castle become the targets of a manhunt that puts both of them in grave danger.