Gibbs and Jimmy respond to a ship when a petty officer dies on board, but when they arrive, the body has vanished from the freezer where it was being stored.
The suspicious circumstances summon the rest of the team, even as McGee and Delilah begin to count down the last couple of months before their wedding.
The victim, Petty Officer Jones, was apparently well-liked and didn't have any enemies with reason to kill him.
His body is later found by the Coast Guard; it had apparently been thrown overboard with weights, but the poorly-tied knots had slipped and the body floated free.
It's found that Jones was killed by MDMA interacting with his blood pressure medication.
Bishop pressures a drug dealer in Norfolk, who gives up the name of the sailor who bought the MDMA from him: Stoddard, the food services officer who found Jones's body.
The MDMA had been intended for the ship's commander, but Jones had eaten the drugged food instead.
Meanwhile, McGee is terrified when Delilah passes out and has to be rushed to the hospital. The doctors perform tests and deliver the good news: not only is she alright, she's also some weeks pregnant.
This inspires the duo to move up their wedding plans. Jimmy gets an online certification to serve as a minister, and performs the ceremony in the apartment, surrounded by their friends.