A casino employee is beaten and raped on her way home from work, but she survives and identifies her attacker. Unfortunately, a DNA test sets him free and Grissom must wrestle with whether evidence can ever lie. Later, Grissom comes to the rescue of a coworker who ends up on the other side of the law
Grissom, Catherine and Nick investigate the death of a runner during a competition. Meanwhile Sara and Warrick investigate the death of couple in a hotel room, initially thought to be a murder-suicide. Both cases take place during this 'cop' competition , with more than 20.000 attendants (all of them cops). This gives the investigations an interesting turn, as almost all the suspects and all dead people are cops.
A mutilated female body is discovered tied to the undercarriage of a bus carrying prisoners from a women's correctional facility after a severed arm flies out from beneath the vehicle and strikes a car. Catherine leads the investigation and at first believes the woman was escaping, but the evidence increasingly points to murder. Back in town, Warrick probes the death of a gambler who was stabbed multiple times in his brother's kitchen.
Catherine and Sara deal with the death of what at first seems to be a transvestite. Later during autopsy they find out that the make-up he seemed to be wearing was actually facepaint, he was a clown. Grissom, Nick, and Warrick deal with the death of a man in a homeless area. They found out he worked in a recovery center for drug users.
Grissom and Warrick get the case of an old woman found mummified in her closet. Sarah and Nick arrive to investigate a breaking and entering to find a raped teen. These cases are not as disparate as they first seem. Catherine looks into a gun found by a boy. The gun is connected to a week old murder across town that Warrick caught.
Two couples meet in a bar and one of the couples is murdered. When a second couple is murdered in a similar fashion the team suspects a pair of serial killers are on the loose. The case is complicated by leaks to the press and a judge reluctant to issue a warrant. Catherine gets some troubling news about her father's murder trial.