The body of a beheaded woman found in a fraternity house is a mystery to the CSIs. Now they must sort through twisted clues and crime scene after crime scene to find the killer that has them trapped in his own little game.

After Flack makes an enormous drug bust, and locks it up at CSI, the drug lords infiltrate the building at gunpoint to get them back. Now the team must resolve the hostage situations, all the while with Mac, Stella, and Hawkes trapped inside.

The most exclusive jewelry auction of the year ends abruptly when an appraiser is killed during the event. The investigation takes an emotional turn when the CSIs must confront one of the greatest tragedies in human history - the Holocaust.

A frantic 911 call sends the CSIs into a vacant penthouse; however, instead of finding the caller, they unearth a nearly 100-year-old corpse and find themselves navigating their way through a booby-trapped house.

When transferring Robert Dunbrook's son from prison to court, the NYPD is ambushed by a group of professional kidnappers who kill a member of the team and one of the CSI's lives hangs in the balance.

The next case takes us back to Dr. Sheldon Hawks' past and the reasons he chose to change jobs in the medical profession. The CSI team may find it extremely difficult to find out who committed the murder of the 19-year-old woman who recently started recovering from an accident.

Reed Garret gives Mac some interesting information regarding the death of a college student. Also the rest of the team will need to be a step ahead of Ava Brandt to figure out why a security guard was murdered.

Community unrest over the police shooting of an unarmed man forces Mac and the team to move quickly to solve the case.

The CSIs are investigating the murder of a hotel concierge, but while doing this they hear gun shots fired across the street and find a woman clutching a gun over two dead bodies.

Danny and Mac have to go to Noah’s Ark to find out if a broken promise leads to his murder. Stella and Sheldon investigate the death of a man dressed as a cigarette. Stella hopes to have her job after not telling Mac that she may be HIV right away.

Illusionist Luke Blade may have to defend the art of magic after an illusion is thought to have killed two people. Back in Montana Lindsay will need to take herself back to the time when she was fourteen to help her remember the crime that killed four friends in order to help convict of the person that killed them.

On the 10th anniversary of 9/11, Mac and the team remember specific moments from that day that were indelibly burned in their mind.

While in Chicago Mac uncovers more clues about his stalker and reveals his troubled past. Meanwhile, in New York the rest of the team is in danger. The hunt is on to figure out the identity of the 333 stalker before time runs out.

When a man takes hostages during a failed attempt to rob a bank, Mac offers himself in exchange for a hostage. Only condition is that he must prove that the bank robber did not kill the bank manager, whose body is found lying in a pool of blood in the vault. On the outside of the bank, the rest of the team works to process the evidence that Mac finds and stop the SWAT team from making matters worse.

In the culmination of a multi-episode mystery, Mac and his team uncover the dark lair of a murderous madman, the Compass Killer. But as they race to save his fourth victim, the sunrise presents one final surprise that no one ever expected.

The team investigates the particularly gruesome outcome of a 21st birthday where the party plans became all but anything worth celebrating. With just a few and not easy answers as their only lead in the case, the CSis are challenged to stretch their abilities to the limit.

A death row inmate's final request brings Dr. Hawkes to a Pennsylvania prison and face-to-face with a tragic incident that he has kept secret for many years, just as a prison riot erupts and traps Hawkes inside.

The CSIs follow a trail left by Shane Casey and realize that he is targeting Danny, who is vacationing out of town with Lindsay and their daughter.

After a hail of gunfire tears through the crime lab, Mac and his ex-partner become part of a vendetta 17 years in the making.

Three women who are dressed as Holly Golightly rob a jewelry store and injure other shoppers in the process. The CSI’s must work through the confusing investigation to hunt them down. Meanwhile Mac has to identify a mummified body discovered in an apartment building that was being torn down.

The next case for the CSI’s gets even tougher when a paintball player turns out to be the prime suspect and later goes missing the team also has another problem the evidence that should point to the prime suspect points to someone else.

After a bartender is murdered The CSI team must prove that Hawkes did not commit the murder. That only becomes more difficult when the team is pulled off the investigation.

Mac believes he can fight the internal affairs investigation that is about to be started against him because of what happened to Clay Dobson. Can Mac explain what happened to the suspect he was chasing and will it be good enough for him to keep his job? Also Stella could lose her job as a CSI after a cold case is somehow connected to her.

Following a near-death experience, Mac becomes determined to close his last remaining unsolved case.

While Mac dines at his local breakfast spot, a gunman opens fire, leaving a waitress critically injured and a man dead, and Mac having to choose whether to chase after the suspect or save the life of the young woman. Meanwhile, before the chaos, Mac was approached by a shy patron who awkwardly engaged him in conversation. After feeling that he saved her life during the shoot out, she asks him to join her for a drink and Mac must decide if he is ready to start dating after his wife's tragic death.