Retired Navy Master Chief "Art Amador" turns on his car in a closed garage after writing a letter addressed to NCIS that read "Had a good run, time to be with my beloved." "Marie Stanhope" who oversees the docent program at the Navy Museum arrives and finds the letter addressed to her from her friend "Art".
He asks "Marie" to take care of "Sonny Lee" and that he donated his rare 1870 S Seated Liberty silver dollar. "Kasie's" research reveals that the coin is the 13th known Seated Liberty coin in existence and the museum can't accept a gift without knowing its origin.
While the team is having a gloomy week, they try and imagine other lives for themselves while going through "Art's" things. "Bishop" finds a love letter from "Annie Downing" and it's flashback time with "Bishop" playing "Annie" and "Torres" playing "Art".
In the present, "Art's" brother confesses that "Art" stole the rare coin. The Seated Liberty disappeared in March 1972, shortly before "Annie" died of a thyroid disorder. "Marie" is disappointed that the museum can't legally take the stolen coin.
However, a new letter from "Art's" collection reveals that he bought "Annie" an engagement ring and her father ended up tossing the ring into the fire. Then another flashback sees "Art" and "Annie" having some kind of fight in a car and two officers pat down "Art" and they find a stick of gum and an old silver dollar.
There may have also been a murder as "Annie's" medical report points to poisoning and not thyroid disease. When they examine "Annie's" body, she's still wearing her engagement ring and it turns out she was poisoned by small daily doses of thallium.
All in all, "Bertha" saves the day and it's "Spencer" that goes to prison as he's the one who murdered "Annie" with the thallium. "Bertha" then donated the coin to the museum and "Art" is reunited with the love of his life.