As NCIS mourns the loss of Ducky, the agents find comfort in working on one of his unfinished cases involving a woman whose father was dishonorably discharged from the Marines.

NCIS comes under attack by a mysterious enemy from the past. Also, Vance tries to mend fences with his estranged son by explaining why, despite the ongoing dangers of his job, he still chooses to stay at NCIS.

When the NCIS team engages in Walk-a-Mile day to gain a new perspectives on different departments, things take a turn when Kasie receives a distress call from a mysterious man.

The NCIS team looks for a motive behind the kidnapping and death of a famous heart surgeon.

The NCIS team must help Torres when he puts his future at stake by confronting the man who tormented his family when he was a child.

With the help of Knight's dad, NCIS works to unravel the mystery of a recently used service weapon belonging to a missing agent. Also, McGee is in a tailspin when DNA results reveal a close relative he was unaware of.

The NCIS team is in a race against time to find a missing officer who disappeared during his wedding proposal.

After discovering a navy pilot's body riddled with unusual wounds, NCIS' investigation draws the team into the rabbit hole of UFO conspiracy theories.

Parker and Knight discover three bodies on an old Navy ship that's about to be sunk and turned into an artificial reef, when they're suddenly locked inside by a mysterious figure. Also, Vance offers Knight a unique opportunity.

After discovering the remains of a Marine captain, the NCIS team travels to Texas to interrogate the suspected killer.