A group of specialists who investigate underwater incidents and accidents called "DCU" newly established by the Japan Coast Guard. DCU is an abbreviation for Deep Crime Unit, and their mission is to hide in all kinds of water, such as "rivers and lakes all over Japan that are extremely dangerous", which is difficult not only in conventional seawater areas but also in police investigations. Find the evidence and resolve the case. Their mission is to "unsolve unsolved underwater cases." While DCU encounters an incident related to "water" and treats human life and preciousness seriously, he draws their human pattern firmly. While drawing mainly on the human drama of the members with rich individuality, we will confront difficult cases such as various underwater incidents, rescue, measures against invasion from the outside, and solve the mysteries and incidents in "underwater" with a sense of speed and exhilaration. ..