When a man is found dead on the Brooklyn Bridge and the only evidence is his marriage proposal displayed in lights on a Manhattan high-rise and a souvenir key chain as a murder weapon buried in his chest, the team comes together to find the person who may have brutally rejected his offer.
The team investigates a jewelry store heist in which 3 women dressed like Audrey Hepburn in "Breakfast at Tiffany's" successfully rob the store. Also, a mummified body of a city councilman's missing wife is found during a building's demolition, and Mac and Peyton argue over the autopsy's findings.
A runner drops dead in the middle of a marathon and the cause seems to be carbon monoxide, Mac and Stella can't reconcile how someone could be poisoned in the middle of Central Park. With thousands of suspects and no witnesses, the CSIs try to collect evidence while spectators and marathon runners contaminate their crime scene. Meanwhile, a high-end vodka's promotional launch party turns deadly, when a model is murdered.
After a sorority girl is found beheaded and hanging from the ceiling at a party, Mac and Stella must track down the serial killer responsible.
Lindsay and Danny investigate the death of a girl who ran away to join the Suicide Girls. Stella and Mac investigate the death of a homeless man who was killed after winning a game.
While investigating the death of a hotel employee at a swimsuit modeling shoot, the CSI team hears shots across the street and wanders onto another crime scene where a shocked woman has just shot an intruder.
Stella investigates the death of a famous bachelor. Mac heads the investigation of a girl found dead in the subway. Sheldon gets in trouble for not revealing his connection to the case.
A professional paintball player is murdered and the team's top suspect is his opponent, but when the opponent goes missing the team must dig deeper to find the killer. Meanwhile, Stella believes she is being followed and Mac worries about an internal leak.
A girl is paralyzed in a car crash and then, after receiving a hopeful prognosis, is murdered in the hospital. Her friend who was also in the car died, so Mac wonders if it was a case of mistaken identity. They also determine that the girl in the hospital had made a death pact with one of her friends. Meanwhile, the investigation at the hospital brings up old issues for Sheldon.
A man dies after his parachute has been sabotaged by pigeons. The team's investigation leads them to the world of pigeon racing and another dead body, a pigeon trainer. Stella investigates a murder of a girl's father at her Sweet Sixteen party. Meanwhile, Mac reaches out to his deceased wife's son.
Sheldon is framed for murder and the team is pulled off the case. Mac discreetly leads an investigation anyway and they discover that Shane's brother is framing Sheldon to get back at him. They must convince Shane that his brother was really guilty in order to free Sheldon.
When an intruder breaks into the home of a deaf family and fatally shoots their teenage daughter, Mac works with the grieving mother who relies on her other senses to provide clues that will help catch her daughter's killer.
Danny, Sheldon and Detective Angell investigate when a man is found dead in the snow with a price tag hanging out from his stomach. The clue leads the detectives to investigate the Idiot-Run race where New Yorkers dress in costumes and race shopping carts from Brooklyn to New York. Meanwhile, Mac and Stella investigate the dead of a real estate agent that appears to be a kidnapping gone bad.
A woman, who turns out to be a man, is murdered after a musical performance at a banquet. Meanwhile, Mac works on a murder of a man found in a sand truck. Lindsay takes some time off to go to Montana to testify.
A college student is found dead in the park and Mac, Sheldon and Detective Flack are suspicious of the college's secret society. The case gets personal when Mac's step son comes forward to provide information about the victim with whom he worked on the school paper. Meanwhile, Stella, Detective Angell and Danny search for the killer of a security guard who appears to be a serial shoplifter.
A music industry mogul is murdered in his penthouse and the only witness is his sister, but her story doesn't make sense. Stella cuts herself while processing the scene and then worries when she discovers the victim was HIV positive. Meanwhile, Danny and Detective Angell investigate the death of a woman found dead in a bathtub with roses.
A man named Noah is found buried under cash after being shot. As Mac investigates he discovers that the Noah had built an ark and sold tickets to people after convincing them the world was about to end.
Illusionist Luke Blade comes to New York in a three night death defying spectacle. When people keep turning up dead in ways that mimic the illusions, Mac and the team must determine who's doing the killing.
When a woman is poisoned at a French-themed fundraiser at the U.N., Mac and Stella run into diplomatic difficulties in removing and examining her body. Meanwhile, a chef turns up dead and Lindsay discovers a jeweled roach a customer was wearing on his body.
When a body is stolen from the coroner's van the team stumbles onto a lab performing genetic testing on human hibernation. The team's two other cases involve a man impaled in a medieval suit and a man found stabbed with an ice pick in his expensive hotel room.
A serial killer whose conviction was overturned due to Mac jailing his arresting officer begins killer again causing Mac to go after him with a vengeance. The team works on a case of a man poisoned by his brother and his brother's girlfriend with Ricin. Meanwhile, Stella gets the good news that she is HIV negative.
Stella is forced to deal with painful memories of her childhood foster sister when Det. Valens shows up claiming her DNA is involved in a Philadelphia cold case.
The CSIs are puzzled when evidence and witnesses point to John McEnroe as their murder suspect despite his air-tight alibi. Meanwhile, Mac's investigation causes a political firestorm, the team worries he'll be dismissed when they are asked to testify.
Following the largest drug seizure in city's history, Mac, Stella and Hawkes are forced to save the lab when, in an elaborate heist, a drug lord and his crew descend to retrieve their merchandise. Meanwhile, Adam and Danny are taken hostage at the crime scene.