Two civilians find the body of a Navy petty officer first-class, submerged in a backyard hot tub; Gibbs and company investigate; Ducky sees an unusual clue. The widow fills in Tony and Ziva, and Abby makes a significant discovery, implicating a ship of the Royal Navy. Gibbs takes a strong dislike to a major in the Royal Marines; however, Ziva asks the major to "do a quickie". Tony and Ziva find an important valve handwheel, and Gibbs gains an advantage by using a pipe wrench. The ship leaves port, but the major stays behind, and the major turns out to be something else, as does a special agent of the CIA. Vance tells Gibbs to cool it; Gibbs takes a different tack, and he finds a visitor when he returns home. The gang trace missing money; they figure out who killed the sailor, and who stole the money, then they nab the person responsible. Tony sets off an alarm.