Hero is a part of a marine rescue team. Just a day before his vacation there is an urgent request to save personnel and cargo of a drowned submarine. The submarine does not have identifying signs apart of the drawing "Doop" and all the crew disappears apart of one member with body half-eaten by mercury reminding liquid. Hero takes sample from the corpse, but the next day one of heroes is found killed by the same mercury reminding liquid. As the team launches investigation, it turns out that there is a criminal/collaborator among the team members...

[From vndbreview]