A biologist, unnamed, sets off on an expedition with four other female scientists, each in a different discipline. There is a psychologist, linguist, surveyor, anthropologist, and the biologist. They will be the 12th expedition to enter into Area X. On their belts are black boxes that will glow red, they are told, should there be any danger. They are not allowed to carry any current technology with them, with the exception of a camera.

The biologist’s husband had been part of the previous expedition, which had taken place two years previously. The psychologist is this group’s appointed leader. They are told that they will not be allowed to communicate with the outside world at all while inside the Area. If something should happen, they are told they should go to the lighthouse indicated on their maps, or meet at the edge of the borderlands and await extraction.

They are all told that because of the hallucinations that other expeditions reported, that they will all undergo hypnosis which will allow them to move through the border lands without incident.

It takes them four days to reach their base camp. There they find a mysterious tower that doesn’t appear on any of the maps they’ve been given. The linguist does not accompany them to the base camp, turning back before they get there. The biologist goes down into a tunnel that they find at the tower. The tower, itself, seems partially submerged. While inside the tunnel the group sees an odd writing on the walls, biblical in nature, but not occurring in any known human bible. The letters house a host of living hand-like organisms that glow. The biologist gets too close and inhales some spores that the organisms release. She decides not to disclose this fact to the rest of the group, who’ve already dismissed her claims of hearing a heartbeat.

That night there is a low moaning noise that they all hear sounding out over the swamps. Later, before they get ready to go to their tents, the psychologist says the phrase, ‘Consolidation of Authority’. Immediately, the biologist notes that the surveyor and the anthropologist’s faces go slack. Quickly, the biologist mimics them. She then sees the psychologist proceed to ‘program’ them to think that going into the tunnels is a good idea, and that they will continue to see a structure made of coquina and stone.

When everyone wakes in the morning they learn that the anthropologist has left the camp. The surveyor tells the biologist that something is ‘off’ about the anthropologist leaving as she didn’t take any of her gear or supplies. The surveyor and the biologist go back down into the tunnels, while the psychologist tells them that she will stand guard at the top of the entrance. The psychologist uses a trigger phrase that makes the surveyor instantly compliant, so the biologist plays along.

The biologist notes that the tower seems to be breathing, that the walls are covered with something resembling a gullet, and that she can still hear the heartbeat as she had the day before. As they descend to the next level they run into the body of the anthropologist, covered in goo and green moss. There are scattered test tubes with samples in them scattered around the body. The biologist picks them up, and then both the surveyor and the biologist leave, quickly.

When they emerge they find that the psychologist has deserted them and has taken most of the supplies and all of the weapons, except one. The biologist puts the samples under a microscope and finds that the cells are a type of brain tissue. When the biologist reports her findings the surveyor says that she’s had enough and they should just leave. The biologist wants to make a quick trip to the lighthouse to see if she can talk sense or get some answers from the psychologist. There is someone or something writing on the walls in the tower. She decides to give that being a name and calls it the Crawler.

The biologist reaches the half-way point, which is an old abandoned neighborhood. She decides to go into one and sees a large bushy grouping of plants that in a certain light, look like a family sitting on a couch watching television. She decides to take samples from them.

When she enters the lighthouse she is shocked to see evidence of great violence. There are splashes of blood on the wall, dark with age, and all of the furniture is riddled with bullet holes. The biologist climbs the stairs and goes into the beacon room of the lighthouse. There is a door to the side of the room and she goes in. There, stacked neatly, some of them rotting away from age, are hundreds of diaries and journals from past expeditions. From the looks of them, there had been more than the 12 expeditions than they had been led to believe.

The psychologist’s gear is stored there, too, but there is no sign of the former leader. The biologist takes an old photograph on the wall and stuffs it into her pocket. It is an old black and white photo of the lighthouse keeper, another man, and a young girl. The biologist goes out onto the balcony portion of the beacon room and enjoys the view it affords. But then, she recoils in horror as she sees the body of the psychologist hundreds of feet below her on the ground.

The biologist grabs some of the journals and additional supplies out of the room, one of the journals belonging to her late husband, and then rushes to find the body of the psychologist. Shockingly, the psychologist is not yet dead, but it is clear that she will be dead shortly. The biologist asks her what happened, and the psychologist says that she tried to shoot the biologist as she came up the path but that somehow she couldn’t do it.

Then, she felt as if she were being chased and she thought that it seemed like a good idea to jump over the railing. She tries to give the biologist a ‘commit suicide’ suggestion, which is the word: Annihilate. The biologist tells her that the suggestions don’t work on her and that they most likely never had.

The psychologist nods and says that she suspected that it wouldn’t work since she could tell that the biologist is already beginning to change. The biologist chalks this comment up to brain trauma from the fall. She asks the psychologist pointed questions about their real mission in Area X. The psychologist will only tell her that the border lands are terrible and that the border is advancing into the city at the rate of a mile each year.

It is nearing dawn when she draws close to base camp. However, before she can get too much further, she feels a sudden brightness engulfing her. She’s been feeling this sensation for a while but at this moment it surges through her and compels her to shift slightly to her left. This saves her life as a bullet catches her in the shoulder instead of her heart. The surveyor is shooting at her. She tells the biologist that she’s figured out that it is the biologist who’s been killing everyone. She tells the biologist that the anthropologist came back to life but that the surveyor had killed her.

The biologist knows that she has been shot and yet the wound doesn’t seem to be slowing her down at all. The pain, in fact, is almost gone. She knows that she has been transforming, but she has welcomed it as it has made her more a part of the surrounding environment.

She is able to sneak up on the surveyor and ends up shooting her. The biologist hates that she’s had to kill the other woman, but rationalizes that it was a matter of survival. She takes the other woman’s body and shoves it into the swamp.

The biologist is hopeful that maybe her husband is alive on an island nearby and determines that she will head that direction, herself, when she is able. The next morning she wakes to find that she is nearly all healed. She takes the samples that she’s gotten from the psychologist’s things and looks at them under the microscope. The moss she’d taken from the figures in the old ruined town end up having human cells in them. She is certain, now, that the military had been doing some sort of genetic manipulation and that it had gone horribly wrong.

Before leaving to find her husband, she feels as if she should come down into the tower’s tunnels one last time. When she does she encounters the Crawler, who motions her forward. The biologist realizes that the Crawler has a partially human face, and that this face is that of the old lighthouse keeper from the photograph that she’d taken from the wall at the lighthouse. The Crawler examines her, then pushes her forward into the deepest regions of the tunnels. Here, the biologist is assimilated into the environment and suddenly understands her connection to it.