Isaac Clark volunteers to go onto the Ishim-Maura or the space ship with technical problems or so they think he only volunteered because his girl friend is on there. When they arrive the crash into into instead of landing correctly, while aboard the ship they run into monsters called Necromorphs. They are the off spring of a planet the Ishi-Maura is what is know as a planet cracker. It cracks open planets and takes resources, what they found on the planet is something called the marker. The marker is what the Necromorphs are after.
While aboard the ship Isaac Clark has't to help fix the ship, later on his girlfriend kills herself because she doesn't want to become a monster. When Isaac goes to destroy the marker he touches it and starts seeing symbols he destroys the marker and its over

Isaac clark wakes up after being asleep for 3 years on the mother ship of the humans. The Necromorphs are back because someone went into Isaac's head and used the symbols to make the marker in the story line it says the Isaac made the marker. for the first chapter your in a straight jacket, until you run into to someone who threatens to kill you and they cut you out then he kills himself. Eventually after killing some monsters and kicking ass, you run into someone who killed his wife and kids (i can't remember his name i beat it a day after it came out). And he see's what Isaac does the steps
Step one: crawl into the dark machine
Step two: the screws go tight, all around
Step three: cross my heart hope to die stick a needle in your eye
Step four: she'll be waiting/ acceptance - final boss
can't remember any but the 3rd he climbs into a machine and you have't to do a mini game with a needle and hit him in pupil.
back the to storyline... After meeting the murder he goes to the lady that has been helping him get there with the promise of a cure for the symbols and she tricks him and then the gun ship comes and kills everyone but Isaac he runs away. After kicking more ass he runs into another woman who runs into the murder later on and doesn't know who he is and calls you and asks who he is with the intention of killing him. You tell her that you need him to survive Later you fix the solar panels and the cable cars and eventually meet back up with them and then you have't to do something else... while your doing that he tries to stab her in the eye and he succeeds and escapes but she survives. Then Isaac runs into his old girlfriend who pops up a lot because he blames himself for her death at this time he only knows 1 step acceptance and he tells her that he blames himself for her death and he thinks that she is good now. Shortly after that he runs into the murderer and he tries to stab Isaac in the eye but Isaac kills him easily. Then you eventually run into the lady again and you go on a drill ride and have't to kill the necromorphs while she's inside the car and your outside and then you crash into the government sector where the marker is and she finds a chopper and gets in it to observer it and you launch the chopper off and Isaac says " I can't let you die like i did with blah." I can't remember the old girlfriend's name and the chopper sends he into space. I can't remember when but earlier than this point in the game Isaac goes back on the Ishi-Maura and has some flash backs, don't waste your ammo and there are necromorphs there I think its at the cable cars if i'm not mistaken. well continuing all of the soilders want to stop Isaac from destroying the marker catch him just run and go up some stairs and he takes out the power core and the lights go out and the solders are killed by thousands of necromorphs You go through some doors and eventually end up at the eye machine where you poke your eye in with a needle, then you continue there are necromorphs that can regenerate because they are within 200 ft of the marker. You have't to race to the marker there are to many necromorphs to fight. And as your walking up to the marker you run into the person who went into your head to get to the information to make the marker he has a gun called the javelin gun and he shoots you, you have't to tap some buttons and you pull it out he shoots you in the hand, then you tear it out and shoot him with his own gun you can finish him off 1 of 2 ways way 1: you just shoot him in the head again Way 2: use the special and electrocute him. After doing that you proceed to destroy the marker and you run into your old girlfriend again and she was never good and takes you into your mind because that is the only way to destroy the marker and she is a memory that is the only way to kill you you shoot her and the black monsters that are hard to kill and shoot the orange bulb that appears and after that you destroy the marker. The building is collapsing and Isaac thinks he has no way of getting out an just sits down. The lady that he launched away comes back in the chopper and a mini game happens because the rocks you have't to climb into the plane with rockets on your boots and you jump into while its flying. And then it ends.