Az epizód ismertetése: Miközben Gibbs a jól megérdemelt pihenését tölti, a csapatából Ziva véletlen szemtanújává válik egy politikai gyilkosságnak. Az ügynöknő így kénytelen alkut kötni az FBI embereivel, majd a nyomozásban is részt venni. Rövidesen azonban kiderül, hogy az FBI Ziva egykori tevékenysége után is nyomoz, ezért az NCIS-nek, Tony vezetésével, be kell bizonyítania a lány ártatlanságát.
Season 4, Episode 2: Escaped
A bank robber escapes from prison and threatens to kill Fornell's daughter if his case won't be re-opened. Gibbs comes to help.
Season 4, Episode 3: Singled Out
An officer is kidnapped, Tony gets an offer he should not refuse and everybody is freaking out about Gibbs's mustache.
Season 4, Episode 4: Faking It
The NCIS team is investigating a Russian arms dealer who shot an officer and Gibbs' mentor Mike Franks comes to help.
Season 4, Episode 5: Dead and Unburied
A marine's body is found inside a new home. The body had been buried, then dug up, and put in the home. His 2 fiancée'es have been receiving letters from him for the past few months. Did one of them get wise?
Season 4, Episode 6: Witch Hunt
On Halloween night a little girl is abducted after her father is attacked. Gibbs and his team must keep searching for the mysterious assailant.
Season 4, Episode 7: Sandblast
A marine officer is killed by a bomb on an Army Navy Golf Course. NCIS and Army CID investigate.
Season 4, Episode 8: Once a Hero
A homeless veteran falls from a hotel room into a party with a lot of High ranking officials. During the investigation they discover a body of a young girl who had apparently been assaulted by the veteran.
Season 4, Episode 9: Twisted Sister
McGee's sister shows up at his apartment, dazed, confused and covered in blood. As he tries to help her, NCIS investigates the death of a sailor on college campus. McGee is conflicted when his job as an investigator interferes with his concern for protecting his sister. The Agents find out about McGee's novel.
Season 4, Episode 10: Smoked
A body falls out of a smoke stack on a Marine base. The FBI tries to take over the investigation when the body is linked to a serial killer who had vanished. Ducky and Gibbs discuss the source of their conflict.
Season 4, Episode 11: Driven
A Navy Lieutenant dies from carbon monoxide poisoning while testing a prototype vehicle. At first it looks like suicide, but NCIS determines that it was murder.
Season 4, Episode 12: Suspicion
When a high-level Marine intelligence officer is found murdered in a small motel room, the NCIS team must find the person who murdered her. After discovering that the person was dead for already three days, and that the town authorities already "investigated" the crime, Gibbs is determined to solve the case, which could be related to a terrorist cell, and not let the town authorities get in his way.
Season 4, Episode 13: Sharif Returns
Sharif the terrorist responsible for planting the bomb in Sandblast is back. Now he's using chemical weapons. A marine is found an apparent victim/test subject for Sharif's latest scheme.
Season 4, Episode 14: Blowback
The secret mission that Jen's been using Tony for finally pans out. She's been pursuing her suspect for a decade. But they'll need the rest of the team, and Ducky to complete the mission.
Season 4, Episode 15: Friends & Lovers
A dead marine leads the team to a Night Club, and a search for a possible serial killer. Gibbs and the Metro Police clash over jurisdiction, and protocols.
Season 4, Episode 16: Dead Man Walking
A navy lieutenant walks into NCIS and asks Gibbs to solve his own murder. He has been poisoned by radiation. While the team investigates, Ziva tries to figure out why the man seems so familiar to her.
Season 4, Episode 17: Skeletons
Some maintenance workers open a crypt, and it explodes. They find some skeletons in what was supposed to be an empty unit. Ducky finds out there multiple skeleton parts, NCIS must track down a serial killer.
Season 4, Episode 18: Iceman
Just as Ducky is about to perform an autopsy, his patient wakes up on the table. NCIS investigates Gibbs finds out an old friend has a personal stake in the matter. Tony's relationship hits a cross roads.
Season 4, Episode 19: Grace Period
Cassidy's team gets a tip on a terrorist plot, when they investigate. The agents are killed by a suicide bomber. Cassidy teams with Gibbs' team to find out who set up her agents. Ducky and Abby find evidence that seems to contradict each other. Gibbs reveals a secret to his team that affects some of his agents.
Season 4, Episode 20: Cover Story
While processing evidence from a crime scene, McGee is shocked when he discovers a link to his newest/unfinished novel. When the team finds 2 bodies, the race is on to find the killer and his link to McGee's work. McGee finally admits he based his characters off his co-workers.
Season 4, Episode 21: Brothers in Arms
Jenny finds a person who's willing to give her evidence of La Grenouille's activities. But her informant is killed. Her behavior is becoming more obsessive, while Gibbs and his team try to help her.
Season 4, Episode 22: In the Dark
A blind photographer takes a picture of a dead sailor. Gibbs and his team must find clues from his other photographs, and from other leads provided by the photographer.
Season 4, Episode 23: Trojan Horse
When Director Shepherd goes out of country, Gibbs steps in as acting Director. That doesn't preclude him from heading an investigation into the death of a person who was on his way to NCIS.
Season 4, Episode 24: Angel of Death
Director Shepherd returns and finds evidence that someone from her past may still be alive. NCIS must undergo polygraph tests, ordered by homeland security. While Gibbs investigates who ordered the tests, Tony and Jeanne face a crisis together.