After his father's death during an explosion at sea 15 years ago, Haruki Senoh joins DCU, a team of crimefighting divers led by Captain Niina, the man who saved his life.

A violent murder rocks the small fishing town of Kita-Noto to its core; local fisherman and anti-poaching activist Ryuhei Shimada has been brutally slain with a giant fishhook.

Sanchez's true identity is revealed; he is in fact Joan Lopez, a dangerous bomber and member of Black Butterfly, an international terrorist organization.

The team is devastated, and the situation is made worse when the DCU is withdrawn from the case. However, this doesn't stop the team members conducting their own investigations.

When the drug-trafficking son of a high-ranking politician is kidnapped, the DCU must tread carefully - a family secret is at stake.

The DCU are called to Yokohama Pier, where the body of a woman has washed up; evidence connects the water inside her lungs and the aquarium the dead woman's fiancé was working for.