What is Dead Space 2 about

If you played the first game, skip this first paragraph and read the second one.
Dead Space is about an engineer sent to repair a planet cracker vessel called the Ishimura, upon arrival, Isaac (the engineer) finds himself surrounded by necromorph monsters. His ship is broken, most of his crew is dead, and he must find another way off the Ishimura. Throughout the campaign you will learn of a relic called the Marker, which can be used to stop the necromorphs, so Isaac tries to get it back on the planet it came from (the one that the Ishimura was mining).

In Dead Space 2, Isaac wakes up to find himself yet again trapped in a horde of necromorph horrors. It turns out they found him drifting in space and took aboard the Ishimura. Obviously, there were still necromorphs on the vessel, so, here we go again. He finds help from a stranger girl (Ellie) and a derranged man (Stross) who rambles frequently about "taking the steps". Isaac is suffering dementia where he can see his dead girlfriend (Nicole), who wants to "make us whole". The dementia can kill him, so when they found him they erased his memory daily. Along his way he encounters the Earthgov who is trying to stop Isaac from destroying the Marker (that he built).