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.

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

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.

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.

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.

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.

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

When an important witness turns up dead, Jo is caught up in the dangerous investigation of the suspected rapist who was freed on her watch in D.C.

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.

Mack and Danny investigate a Marine found dead in Central Park during Fleet Week. The evidence doesn't add up and who is Ellie? Stella, Lindsay, and Hawkes investigate a dead body found in a burnt out car. The results of their investigation leads to a devastating loss for the whole team.

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.

A Russian tourist is found stabbed to death and the CSIs come face to face with the frightening realities of human trafficking. Solving this case becomes personal when it directly affects a prominent member of the NYPD

A lethal pipe-bomb blows a Manhattan townhouse and valuable evidence to pieces, forcing the CSIs to get creative in reconstructing the damaged clues that ultimately lead to the bomber.

The Compass Killer is back, and adds yet another to his circle of victims -- but this time the CSI squad knows his name; Flack's alcoholism threatens to derail his career...

When a woman's body washes up at the South Street Seaport, the CSIs unravel a dark secret from Deputy Chief Carver's past that threatens to shatter his stellar reputation and close-knit family.

When the CSIs track down a suave and charming hitman, their investigation uncovers a conspiracy with far-reaching implications.

Horatio Caine follows Henry Darius to New York so that he can keep his promise to a young boy in Miami, but by the time he and Mac are able to locate Darius he has disappeared again, leaving behind six more bodies. The crossover starts on CSI: Miami S04E07 Felony Flight (I).