When a Japanese sailor is killed on American soil and evidence links the case to the previous murder of the victim’s girlfriend back in Japan, NCIS must find the murderer before the wrong person is accused and the case triggers a diplomatic crisis.

When an anti-capitalist protestor is murdered, Jane and the team investigate and find themselves caught in a war between eco-activists and a tech billionaire fighting over a piece of land. Also, Jane and Captain Joe go on a date.

The NCIS team investigates a cold case involving WWII-era bones on the 80th anniversary of the Pearl Harbor bombings, and are shocked to learn they belong to a 100-year-old survivor of the attack.

When NCIS investigates the mysterious death of a Navy engineer, Joseph Chan, they learn the last person he met with was his colleague, Maggie Shaw, Jane’s mentor and friend, who’s been kidnapped. Also, David Sola, a New Zealand intelligence service case officer arrives in Hawai’i, following a lead that connects Joseph’s death to a Chinese black op secret agent.

While Jane is questioned following Maggie Shaw’s arrest, the rest of the team investigates a mysterious case of Marines with damaged ear canals from a weapon that emits ultrasonic waves. Also, Ernie visits his friend, Dr. Tony Lee (Alec Mapa), to identify possible suspects who had access to his classified weapon.

NCIS Agents Nick Torres and Jessica Knight travel to Hawai'i when they learn a key witness in one of their old cases has turned up there with crucial evidence.

The crossover starts on NCIS S19E17 Starting Over (I).

The NCIS team investigates a shipwreck carrying exotic animals that now threaten the native wildlife on Oahu. Also, Alex sustains a career-ending injury and Kai asks Melanie, a fish and wildlife agent, out on a date.

Captain Milius returns to Hawai'i for a secret prisoner exchange operation and brings in Jane to be his personal security escort in the Philippines, where the exchange will take place.

Captain Milius continues to work with Tennant and her team in the aftermath of the prisoner exchange between U.S. and eastern Europe. Also, Whistler takes Ernie's advice and makes a grand gesture in the hope of winning back Lucy.

Tennant’s team, along with NCIS agents Nick Torres and Jessica Knight, track The Raven’s whereabouts to the island of Oahu and learn about his plans to attack RIMPAC (The Rim of the Pacific Exercises), the world’s largest international maritime warfare exercise.

The crossover starts on NCIS S20E01 A Family Matter (I).

The NCIS team's investigation takes them deep into the world of illegal street racing after a Marine staff sergeant's body is discovered in a junkyard. Also, Tennant is concerned Alex is hiding something from her, and Whistler is anxious about introducing Lucy to her co-workers.

Tennant and the NCIS team suspect foul play when they investigate a fatal car crash involving a Navy officer who turns out to be an imposter. Also, Whistler finds herself in danger when she goes undercover to learn the truth behind the accident.

When a Navy sailor washes up dead in a sacred, forbidden kapu site, the NCIS team brings CGIS Special Agent Pike to unmask the mystery and catch a possible serial killer on the island. Also, Tennant meets Alex’s new girlfriend.

When a Marine corporal dies in a tide pool after being exposed to fentanyl, the NCIS team must quickly find the source of the drugs; Alex talks to his parents about taking a gap year; Ernie reveals personal news to Lucy.

When Commander Chase is abducted from her home by an Army Ranger accused of murder, the NCIS team must act quickly to find her and the suspect.

When an elite special forces Marine captain is murdered, the NCIS team finds a suspect in a really unusual place.

When the murder of a captain and his wife echoes a previous case, the NCIS team brings in a former team member to help determine if they are dealing with a copycat killer.

When a Navy deserter accidentally comes out of hiding, his family becomes a target that drives the NCIS team and Charlie 1 to investigate who is after them. Meanwhile, Lucy surprises the team by returning to Hawai'i from her agent afloat job early.

When Tennant interrogates a suspect during his helicopter transfer and the helicopter crashes, she must utilize her skills to save herself and the other passengers.

After the mysterious death of an astronaut in a highly sensitive Mars simulation, the NCIS team must send Ernie into the habitat to investigate alone.

When Lucy receives a strange call on night watch from a man admitting to murder, the NCIS team sets out to find him.

When a figure from Tennant’s CIA past re-emerges, the NCIS team seeks help from the most unlikely place to catch a killer who threatens to destroy everything Tennant has built.

Following the crash of a prisoner transport plane, the NCIS team must find the convicts that escaped onto the island. Meanwhile, Sam Hanna and Tennant are tasked with locating a high-profile Russian prisoner known as "The Chemist".

When a Navy pilot is found murdered at a local military resort, the team goes undercover to discover a criminal enterprise hiding in plain sight.

When the fiancée of a vanished naval officer seeks the help of NCIS, the team reveals his secrets go much deeper than she suspected. Meanwhile, Sam recruits Kai to be his wingman.

When a Marine is murdered during training on the Big Island, the NCIS team tracks the suspect deep into the woods and discovers a disturbing secret.

After a Marine's wife is kidnapped for ransom, the NCIS team uncovers dark secrets as they race to track down her abductor before it's too late. Meanwhile, Sam seeks Ernie's expertise decrypting a computer program that may have deadly ramifications.

When a high-value bioweapons expert is murdered in a secure facility on Hawai'i, NCIS and the NCIS Elite team join forces to track down the killer and discover an even deadlier threat.

Following a devastating ambush with a deadly bioweapon, the NCIS team must track down a mysterious terrorist group before they can strike again.