It's the year 2017. The planet Earth sets up a research station, Vita Base, on Mars with the mission to discover if life did exist there. After a discovery there comes one last garbled message—danger, danger cliché approaching--“have opened Pandora’s box… all the evils of old Mars have flown out,” and a warning, “…if you do send a manned mission, warn the crew…Stay Alone, Stay Alive…” then nothing. So now it’s 2018, and your rescue mission to Mars crash lands. When you get to the base, the welcome wagon is made up of zombies and an alien virus that will make you look back fondly on the days of the Black Plague.

You control a team of three: Kenzo, Karne and Matlock. They enter the base from different airlocks and try to discover what happened. The reason for the whole "Stay alone, stay alive" warning is that if your team members come together they end up forming into a disgusting mass of flesh -- picture the thing from Leviathan -- called a Trimorph.

As you proceed though the base you find clues as to what occurred. In addition, you run into Trimorphs, some of the non zombiefied former base crew, that are bent on your destruction. They come in two sizes -- the small spidery kind which hack at your shins and jump on your face or the huge "better run like hell" monstrosities that will tear you to pieces.