The episode starts on the sea with a group of people on a boat having a good time. One of the folks went diving only to find out that there is a dead marine underneath the ocean. The name of the marine is seaman Russell McDonalds, 19 assigned to USS Foster.
The marine is still dressed in his uniform with 25lb weights chained to his body that kept him from floating. Aside from that he had a sword, something used decades ago in history.
Dinozo and Kate interviews the mother of the marine and confirms that his Son is God fearing and would not kill himself.
Gibbs, Kate and Dinozo goes aboard the ship of the killed marine and sets up office inside a room. Kate was surprised after learning they are sleeping in one room and Gibbs volunteers for the couch. NCIS now starts their investigation on the ship.
One initial investigation, everyone says that the marine kept to himself and people didn’t know much about them.
In the meantime, Abby has figured out that the marine is connected to an online game he is playing and the other people who he is playing against are from the same ship—USS Foster. Dinozo went to Puerto Rico to find out where the marine bought his sword and find out it was sold to other marines for a higher price since it is illegal to sell weapons to marines. Gibbs found the person the marine was playing online against and thought they decided to take the game to the next level—real life.
The marine whom McDonalds played against confessed they played in real life since McDonalds was so pissed off he lost most of the time. Kate who is a devout catholic cannot believe that the marine who is also a catholic killed himself. Kate read the diary of McDonalds and on the last chapter he was going to release a plague in the realm. Gibbs figured out that McDonalds was going to detonate the USS foster with a chemical biological weapon especially because he has knowledge of it.
It turned out that the plan of McDonalds was to release a virus on the computer game and kill the skipper of the ship. NCIS was able to stop it and it was learned that McDonalds killed himself unintentionally by wearing his uniform, putting on the sword, and weights and going to see convinced that he could walk in the water since he was Immortal. This proves how screwed his judgement is, not knowing the difference between a video game and reality.
The story ends when Dinozo gave Kate bikinis as a present from Puerto Rico and Gibbs a video game book; unfortunately, it was in Spanish.