Plague

For the removed mechanic, see The Sickness.

This article contains major spoilers. Reader discretion is advised.

The Plague is an illness caused by exposure to the airborne spores of the Being and appears capable of affecting many forms of life, limited not only to people and animals but potential plants as well (deformed broken trees can be found throughout the forest). There is potentially a supernatural aspect to it as well, but equally possible is that its unexplainable effects are linked to the alien biology of the Being. The concentration of these spores are elevated at night, to such a high concentration (750/m³) that exposure by non-acclimatised individuals is fatal - these levels fall to >50/m³ during the day (exact unit of spores per unit volume not specified). The link between the Plague and essence is less clear, but it appears to the temporarily intensely amplify the auditory and visual hallucinations caused by infection. Essence could be a liquid form of the spores. All Outsiders working in the forest are required to wear hazmat suits in order to prevent infection, their bodies still wearing these hazmat suits can be found in multiple places in Chapter 2 (helicopter wreckage, and the campsite near the road home), additionally an unworn hazmat suit can be seen in the locked container outside the Dry Meadow hideout, and are referenced in a note left by previous expedition.

Once infected, the host will experience a multitude of mental and physical symptoms, which in later stages is often (but not always) accompanied by horrific mutations, which ultimately result in the host either becoming a 'protector' or 'worshiper' of the Being, or results in the host's body completely breaking down, decaying and filling with toxic gases (potentially spores) further spreading the disease.

It is important to differentiate the effects of the plague on the organic matter from the replication process of the White Substance by the Being. Both frequently result in a deformed/mutated organism, but their processes are very different. The key difference is that the plague mutates a host body, whereas the white substance replicates a host body creating an entirely new entity.

Plague: The original host body retains much of its original gross morphology (mutated humans will look like humans, mutated dogs will look like dogs, mutated pigs will look like pigs), where physical mutations do occur they can only distort what is already there. The host body may grow uncontrollably and disproportionately (the Musician; the Pretty Lady; the Sow), sometimes there may be additional growths, especially teeth (the Musician, Chompers). At its least extreme in humans, the Plague may cause only minor physical changes (Savages), at its most extreme the body may split in half down to the waist (Chompers); in dogs the end result is not quite as extreme (Huge Dogs). Plague carrying enemies in the game consist of Savages, Chompers, and Huge Dogs. All inhabitants of the woods are infected with the plague, but most of the villagers have still not yet fully succumbed.
White Substance: The lifeblood of the Being, this liquid substance runs throughout the forest through the immense network of roots. Normally not visible at the surface (though it can be observed on the cracked surface of the "Road Home"), this substance can be observed and commented on by the Protagonist in some of the Outsider tunnels, if the Protagonist breaks off a branch from the Talking Tree, and again is mentioned in Outsider notes as having "shape shifting" properties which it loses once disconnected from the root network. This substance functions both as a method of growth and repair for the Being, and is capable of taking the shape of anything it comes into contact with (most notably trees, only 15% of the woods at the time of the game is thought to still consist of real trees), and grows at a remarkable speed, such that trees that have been cut down can regrow almost instantly. The White Substance does not only replicate trees, but other objects too, both organic and inorganic, sometimes merging the two. It is unclear if on some occasions this may be intentional, as with the case of Banshees, Human Spiders, Centipedes, and Swampers, shrines (assembled by the Savages) can be observed in the Swamp, where humans and other animals have deliberately been placed in close proximity for the roots to bind - new half formed bodies of these creatures can be found half emerged from the ground around the Swamp. Once the White Substance has a template, it will begin to replicate, sometimes creating only one copy (e.g., Wolfman, Trader, Mushroom Granny) sometimes it creates multiple (the Snail, the man in the tunnel, the frozen savages on the Road Home) which can be found in close proximity to one another. Replicas/clones appear to be immune to the Plague and also to the call of the Being (with the notable exception of the Snail; though it is possible that this is a result of it's original human body's mind having already deteriorated signficantly from the plague, and when the body was copied the desire to find the Road Home was duplicated as well).

It appears that the Plague could not persist beyond destruction of the Being in the True Ending, but it is stated in the transcript that the mental symptoms completely vanished upon its death, suggesting that like the White Substance losing its shape-shifting abilities when being disconnected from the "arteries" (roots) of the Being, the Plague also lost its hold once the heart of the forest (the Being) stopped beating. What this meant for White Substance derived beings is unclear, all characters that the Protagonist meet that were created this way die from the flames or die prior to the fire starting, the lone exception being the Wolfman but he vanishes leaving his fate unknown.

Backstory

The Plague's origins can be traced back to the Being crashing to Earth in August 1975, but it doesn't appear to have begun to notably problematic for the first few years. Conversations with the Villagers seem to imply the Plague began to manifest ten years before the start of the game, placing the Plague's origins sometime around 1977. According to the Cripple, around this time the trees began to rapidly grow. This seems to be confirmed by Mushroom Granny's fourth and fifth paintings. During the late 1970s, the Being quickly began to grow, this growth caused localised flooding (unclear why, but perhaps its growth disrupted path of a local river? A dry river can be found in between Silent Forest and the Old Meadow). In addition to the flooding of fields, the village closest to the Being, humans and livestock alike, began to become affected by the plague. The Doctor, originally a normal local doctor, was quickly overwhelmed with cases, and was unable to help the villagers, for which they would grow to resent him.

After a few years, the Polish government (Outsiders) began to intervene. Infected livestock and houses were burned by helicopters, and evidence of a significant military presence can be found throughout the Darkwood. Some inhabitants of the area were evacuated, but at least two villages remained inside the Darkwood. At least two checkpoints were established on roads leading out of the area, although the roads and gates were eventually completely consumed by the forest, completely cutting the Darkwood off from the outside world by 1983. The Outsiders arrived in the area shortly after, digging tunnels underneath the region and monitoring the situation remotely. Not wanting to risk contagion or spreading of the Plague, the Outsiders decided not to attempt to further help the inhabitants of the woods, and would instead shoot anyone attempting to use their tunnels to escape the region.

Eventually, even the tunnels became gradually crushed by the expanding root networks of the Darkwoods. At least one (Tunnel 22) of these tunnels is known to have collapsed, while the tunnel the Protagonist travels through, Tunnel 21, is close to it. By the game's start of 1987, all Outsiders have either been evacuated or killed, except for Protagonist and Maciek both of whom are already infected by the plague.

Effects

Almost all life encountered in the Darkwood can be infected by the Plague. It is responsible for the abnormal growth of the trees, vines and fungi across the Darkwood, for creatures such as the Huge Dogs, Huge Bugs and the Sow. The Plague seems to affect humans differently on a case by case basis. Its symptoms can manifest gradually over a period of years or within a few days. Some gradually lose their minds and become Savages, a process the Doctor will undergo if he remains alive in Chapter 2, while others such as the Madman or the Musician seem to be in the process of transforming into Red Chompers.

Though some individuals such as the Pretty Lady and the Protagonist have unique mutations, the Plague seems to manifest in two different ways in humans. The first manifestation will usually result in the creation of a Red Chomper while the second will result in the creation of a Savage. Some of these symptoms can also manifest in non-human lifeforms.

Symptoms of the first variant include (Mainly Physical Mutations):

Abnormal and accelerated growth, often asymmetrical and resulting in severe deformities (The Musician in chapter 2, Hanuska's child and the Pretty Lady. Can also be seen in Huge Dogs.)
Partial or total hair loss (The Musician, Madmen and Red Chompers. Seems to be present in Huge Dogs as well. The Protagonist also seems to have lost some hair judging by their naked sprite in the True Ending.)
Splitting headaches. Eventually, a scar will appear on the center of the forehead and gradually widen and lengthen down the body, while teeth develop on the inside of the body (The Musician in chapter 2, the Madmen and Red Chompers seem to be different phases of this process)
Mental state still seems to deteriorate but slower in comparison to second variety. The Musician can converse easily with the protagonist, while the Pretty Lady and Madmen are still capable of one-sided conversations.

Eventually, whether out of pain or their deformities becoming too severe, these infected will stop moving and fall into a sleeplike state (Sleeping Red Chompers and the Musician's Parents), during which they will complete their transformation.

Symptoms of the second variant include (Mainly Mental Deterioration):

Obsessive-compulsive behavior - will often be drawn to covering themselves in mud and sticks, drawing strange symbols, or a compulsion to eat mushrooms or tree bark.
Auditory and visual hallucinations (The Protagonist throughout the game seeing or hearing himself and his dreams, the Doctor hearing the voice of his daughter, the infected villagers in the Silent Forest, and several other characters also hear voices)
Insomnia and loss of appetite (The Protagonist, the Doctor)
Heightened aggression (The Protagonist, the Doctor, and the Savages themselves)
Partial or total loss of ability to write (The Protagonist in their first Journal Entry, Doctor in Chapter 2 - his Journal)
Decrease or loss of speech (The Protagonist, the Doctor in Chapter 2)
Lack of self-preservation (The Doctor indifferent to losing teeth in Chapter 2)

Eventually, these infected seem to abandon their homes or camps entirely, embracing the lifestyle of a Savage. Savages seem to avoid non-infected but occasionally can be found in groups with each other. Savages seem to practice ritualistic behavior by drawing markings, tying corpses to trees and placing the corpses of animals and humans in bizarre arrangements.

Infected that give in to their desire to return home often end up wandering deeper and deeper into the forest. These people will often end up becoming Sleepers, spending their last days in a euphoric dream as they are devoured by the Forest. The Infected wishing to head for the Road Home is more common with the second variant of the Plague, but those suffering the first variant may also on occasion suffer this symptom (The Musician if left in Chapter 1 if both parents dead + Bliss Ending).

Epilogue

In the True End, it is made clear that the Protagonist has not escaped the Forest, but has become a Sleeper, trapped amongst hundreds of others in a massive tree, at the heart of which lies The Being, the source of the Plague. The Protagonist is left with the choice to succumb to The Being's influence and fall asleep within the dream to achieve the Bliss ending, or uncover the facade and wake up to achieve the Burn Them All ending.

In latter ending, the Protagonist will retrieve a flamethrower from another Sleeper and former Outsider, Maciek. They will then proceed to set The Being and the heart of the Forest on fire, killing themselves and hundreds of other sleepers in the process. With the death of the Being, the Plague dies with it.

See Endings and Transcript.