You open the closet with your gun aiming toward it. Inside, you find a panicking scientist, who yells when he sees you.

"Wait, you... you're human, aren't you?" he says.

"Yes," you respond.

The scientist looks relieved and stands up.

"Thank you. It seems we are on the same side then. We're going to have to work together if we want to get out of here alive."

"What's the situation here?"

"Alright. I guess you should know."

The scientist says, "For the last few years, we've been working on something called the Reanimator. It's a small symbiotic organism that enters and feeds on our blood. It doesn't drain enough to have any actual impact on people, at least not when it comes to blood quantity. In return, the Reanimator does what it is named after and reanimates dead cells within us. With this thing, the average human age could become more than three hundred years and it would completely wipe out any known diseases."

"I'm guessing it doesn't work quite like you had hoped," you say.

"You've got that right. Subject Zero, the subject we had infected with the Reanimator, seemed to be uncontrollably violent and mutated for some reason. The Reanimator seemed to be greedy and wanted more blood to feed on, but if it killed its host, it would die. So it caused a mutation. Why that is, we have no idea, but the Reanimator took control of the host and mutated Subject Zero to make it capable enough to escape its confinement and feed its hunger."

"It started eating people?"

"Yes. And with it, it contaminated the corpses with Reanimators as well. Now, all the dead people in this godforsaken place are mindless slaves to the Reanimators and constantly thirst for blood. And then there's Subject Zero. He's out there somewhere. I saw him enter the ventilation systems. We should stay away from the vents."

"How do we stop it?"

"In Subject Zero's cell. We have a bionic weapon there that specifically targets Reanimators and annihilates them. It makes the air poisonous for them."

"Wait, there is a monster out there, and you want me to go to its home?"

"Not its home, but otherwise, yes. You can choose to leave, but I'm going to try to kill it, with or without your help."