On NCIS, A Navy seaman wakes up for her 3 am duties on the U.S.S. Hoover but is interrupted by her mother, who has joined her on a Tiger cruise for families to join their servicemen and women family. After getting her mother back to bed, she goes to do her job at the trash compactor when she notices that the compactor stops working. When she investigates, she finds blood and a body.
Back at NCIS, Tim is going over his proposal with Ellie. It involves mathematical symmetry and everything. However, Ellie points out that based on his idea, he won’t be proposing for six months. Nick notices that Tim is nervous and points out that if he notices, his girl will notice.
Gibbs interrupts to let them know about the case. Quinn joins when the other three refuse to go on a destroyer. On the U.S.S. Hoover with Gibbs and Palmer, Quinn realizes the commander recognizes her. They find out only one person has not answered their post and go toward the scene of the crime.
While Jimmy examines what he can of the victim’s remains, Gibbs find a wooden stick used for the compactor that could be the weapon. The commander arrives and the victim is identified as Lieutenant Vivienne Mills. She has a Tiger who is looking for her, a cousin named David Kemmons. They go to let him know about the murder, but discover the news has already made its rounds on the ship.
A celebrity singer named Kacey Powers had been on the ship for a Goodwill tour and tweeted about the agents being on board. Nick, Ellie and Tim discuss the hashtag #MurderBoat before Tim goes to Ellie for help. He wants her to hold onto the ring for him so it does not make him nervous. She doesn’t want to hold it because she will be having lunch with Delilah. Tim begs her for help and asks her to “be my Frodo.” Ellie gives in and agrees to hold onto the ring so it doesn’t occupy his mind.
Gibbs and Quinn interview David, who was Vivienne’s only family. He is devastated, but is annoyed when he feels he is being interrogated by the agents.
Through his laptop, Jimmy discusses the body with Ducky, who had not come due to food poisoning. Jimmy knows without an autopsy there’s not much he can tell Gibbs. However, Ducky noticed from crime scene photos that she has a piece of metal embedded in her arm. Jimmy wants to know if they can identify it so Gibbs doesn’t get mad when he can’t answer that inevitable question. Abby comes to the rescue to tell them it is likely an antenna.
Quinn and Gibbs go through interviews, including with a man named Merrick Gomer. He claims he was getting seasick all night. There’s even proof from his phone since got sick on it and it broke. They interview plenty of people but don’t have any leads to a suspect.
They notice a fight going on between Curt Shapiro, Kacey’s press agent, and a man who claims to be getting an autograph for his daughter. After calming the situation, they see Jimmy, who tells them the commander wants to see them.
The commander lets them know that a man named Stewart Baxter did not check in and he is one of the Tigers. His sister, Jennifer, comes in to tell her commander that her brother never even got on the ship due to car trouble. There is an imposter on board.
After calling her brother to go to NCIS to speak with them, Baxter’s sister is upset that it looks like she is involved. Quinn assures her they will work on solving the case.
Tim is nervous about where Ellie plans on keeping the ring. As they discuss it, Delilah arrives for lunch and he does a horrible job playing it cool. After making her feel suspicious, Nick rescues him by flying a drone into the bullpen. He lets them know the antenna on the body came from a drone that was apparently on the ship.
Quinn tries talking to David again over cards, but he does not appreciate being interrogated. He did have experience with drones but wants her to find who killed Vivienne and stop questioning him.
In the NCIS garage, Abby confirms to Nick that Baxter did have car trouble and he did go to have it fixed, but the job was sabotaged. Someone made it so he couldn’t get to the ship.
Quinn tries to interview Kacey, but things don’t go well. To add further to their dilemma, the commander wants to dock the ship even though Quinn and Gibbs worry their killer will escape.
Ducky and Palmer look over the body and conclude she had been hit in the head with the weapon Gibbs found. Palmer admits to Ducky that he vomited on their evidence bags. Ducky assures Palmer he still did his job.
Abby talks to Tim in her lab and congratulates him on asking Delilah to marry him. Then she tells him that part of a drone was found in another trash area and it had a camera. They are able to see that someone filmed Kacey Powers in restricted areas of the ship.
Quinn and Gibbs talk to Kacey, who reveals she is having difficulty with her vocal chords and has to rest her voice. She wanted to do the Goodwill tour for good publicity, especially since her grandfather was in the service. But she tells them their camera and things were confiscated. An unknown individual was filming her.
Ellie suggests hiding the ring in her desk, but Tim says not to and he’s broken into the desk before. At her shocked expression, he tells her it was during his time with Kate and Ziva. Brave boy, Tim.
The team gets security footage from Baxter’s movements when his license was stolen and they learn the “father” from the ship was the one who took Baxter’s license. Before Quinn and Gibbs can find him, a man goes overboard.
Once they get Wayne Cribbage at NCIS, he admits that he is a paparazzo who was following Kacey. He had nothing to do with the murder, but he did witness it. His drone was in the trash because he was trying to hide when a man and woman walked in. They argued and he ran once the man left.
Gibbs is frustrated that no one knows who their killer is. Just then, Tim’s computer beeps. One of the men they questioned, Merrick Gomer, has a restraining order against him from his ex-wife, who he has a son with.
At a park, the boy’s babysitter is confused about Merrick picking him up. When Merrick gets in the car with him, NCIS arrives before he can drive off with the boy. Tim arrests Gomer while Gibbs distracts the child.
Tim and Quinn interview David to tell him about the killer. Vivienne was friends with his ex-wife and recognized him. She was going to report him for being on the ship. It is then that Quinn reveals she knows he is really Vivienne’s boyfriend. She had dug into his background and a necklace found on the victim’s body was given to her from him. He tells them he had convinced her to let him come and the next cruise for significant others wasn’t for another six months.
When he says he wished he had gotten her a ring, Tim excuses himself to rush out of the building. He takes the ring from Ellie’s desk and goes to the elevator. Seeing Delilah when the doors open, he asks the man beside her to give them a moment and gets in. Shutting down the elevator, Tim gets down on one knee and proposes. She says yes and they embrace.