After a routine call leads two of the team into finding a bomb, they evacuate but a few are still in the building along with Mac and Flack when the bomb detonates. After the explosion the CSI's face a race against time to find the bomber and the possibility of losing one of their own. Mac must come to grips with having let a Marine die in Beirut in 1983.
Two women both claim to be the wife of a murder victim surprise Mac and Stella at the circumstances of their relationships. Both women have been in a trinogamous marriage with the victim. Meanwhile, Danny and Lindsay investigate the murder of a young woman who is found off a dock tangled up in kelp while she is dressed as a mermaid.
Mac receives a phone call confessing to an old murder before the caller commits suicide. The call leads the team to a football stadium to uncover a body and they learn the suicide victim belongs to the Tanglewood gang. They also find a cigarette that puts Danny's job on the line after his DNA is found on it. Stella and Danny investigate the death of a businessman who used the services of an expensive call girl service.
Danny and Stella find innovative ways to process a crime scene while Danny is trapped in a panic room with the victim, who was the only person with the security code. As a locksmith works to cut through the titanium doors, the CSIs rush to process the evidence before the victim decays further and Danny's oxygen runs out. Meanwhile, Mac, Dr. Hawkes and Lindsay investigate the murder of an exotic dancer found dead on a klieg light
When a man is found murdered in an elevator, Mac, Flack, Danny and Lindsay investigate a world where very young girls enjoy sexual encounters with much older men. They're left trying to determine whether their best lead is a suspect, a witness ... or the intended victim. Stella and Hawkes investigate the death of a young man found in Central Park who died from an extreme allergic reaction and learn that he had been pretending to be someone that he wasn't.
Mac, Stella and Flack investigate the death of a young dancer who recently won the lottery, and it isn't long before they realise that her death is connected to Lindsay's investigation concerning the death of a tram driver. Danny and Hawkes look into the murder of a local fish merchant, and soon find their way to a jealous friend who was angry that their child didn't get into a prestigious school.
Mac and Danny look into the mysterious death of a man torn apart by tigers at the Bronx Zoo, which leads them to both the dead man's meat packing plant as well as his mafia relatives. Hawkes and Stella are left with the case of a beautiful young debutante found dead on the carousel only hours before her coming out.
Stella and Danny are heading into the world of cuddle parties: non-sexual events were adults learn to touch and hug each other. Meanwhile, Mac, Hawkes, and Flack investigate the death of a hated plastic surgeon found covered with lye with thousands of eyewitnesses during rush hour at Grand Central Station. While Mac and Stella assist Aiden in a rape case, after she breaks an evidence seal, Mac must come to terms with Aiden's action and work up the nerve to fire her.
Stella and Danny investigate when a jewellery designer is found dead, wearing the eight million dollar bra he created, and investigate the model he had shot and her bodyguard. Aiden begins to take the rape case she has been working on a little too personally, and is determined to stop the man before he can rape again. Hawkes gets to go into the field for the first time as he assists Mac in investigating the death of a man who liked to climb skyscrapers.