Navy therapist Dr. Gabriel Lin is jogging with a friend when he collapses. Diagnosed with fatal poisoning from polonium-210, he goes to Agent Pride and the NCIS team to discover who has killed him.
Dr. Wade performs a live autopsy to determine how long ago Dr. Lin was poisoned. One potential suspect is Dominic Cole, a former member of the Coast Guard who was dismissed from service at Dr. Lin's recommendation.
CGIS Agent Borin arrives to help the team locate and capture Cole. After a pursuit, they take him into custody, but soon learn that he isn't the culprit.
They locate the source of the polonium: it had been injected into the toothpaste at the loft of Dr. Lin's late father, throwing suspicion on Lin's estranged brother, Cam, who is involved in a lawsuit about their father's land back in Taiwan - land that has skyrocketed in value due to a company's interest in developing it.
Cam denies having any contact with the developer, and the team executes a search warrant at his house. They discover, to their shock, that Cam's water was also spiked with polonium. Sebastian is able to discover where the polonium came from: it was sold to the company that is owned by Cam's wife's father.
They arrest Cam's wife, who was bitterly resentful after Cam's poor investment burned through all their money. She wanted to sell the land to the developer and make a fortune, thus returning to the life she had always wanted.
As LaSalle goes off on a skydiving trip with buddies, Brody contacts Dr. Wilkins and agrees to go out for coffee with him, and Dr. Lin and his brother, now repairing their relationship, go for one last run before the end.