Admiral Clifford Chase (who previously appeared in NCIS Season 8 Episode 7, "Broken Arrow") falls victim to a particularly devious piece of malware known as ransomware.
He summons McGee and informs McGee that he will not pay the demanded ransom to unlock his computer, and instead insists that McGee work to fix the problem instead.
McGee only becomes sufficiently motivated after Chase intentionally infects the teams' phones with the ransomware, too, much to their frustration andthe annoyance of Director Vance.
A colleague of Reeves directs them to a CIA anti-ransomware specialist, who vanishes the moment their backs are turned. They soon learn that the specialist, Clint Asher, actually created the virus in college.
Asher later turns up dead and deep-frozen in a lake. He was frozen by a very large amount of liquid nitrogen. They eventually trace the liquid nitrogen back to Asher's former college roommate.
The ex-roommate was using the liquid nitrogen to conduct fringe-science experiments on cryopreservation, funding his out-there "research" with the ransomware payments.
The team arrests him for the murder and the cyberterrorism and he deactivates the ransomware on the systems.
Meanwhile, Quinn handles painful personal matters as she realizes that her mother's mental state is deteriorating, with her mother forgetting things like her father being dead for three years, and even her own neighborhood.
Quinn decides to move back in with her mother to look after her.