A killer lurks beneath the waves of the western Pacific Ocean. The USS Encinitas, the first attack submarine crewed by both men and women, stalks the Crescent Moon, a renegade Iranian sub armed with nuclear-tipped missiles. But another predator hides aboard the American sub, a murderer who has already left a trail of dead women behind on shore. While the crew of the Encinitas plays a deadly game of hide-and-seek with the Crescent Moon, NCIS investigator Linus Schag must discover the killer’s identity before his – or her – blood lust leads to the submarine’s total destruction.