S5E4 · Detour

Two men are surveying an area of the Apalachicola National Forest in Leon County, Florida when they are attacked and killed by unseen assailants with glowing red eyes. Later that day, Michael Asekoff and his son, Louis, are hunting for opossums with their dog, Bo, in the same stretch of woods. Upon discovering a surveyor's bloody jacket, Michael orders Louis to take Bo and run home. As Louis and the dog head off into the woods, two shots are heard.

Meanwhile, Fox Mulder (David Duchovny) and Dana Scully (Gillian Anderson) are carpooling with FBI agents Michael Kinsley and Carla Stonecypher en route to a "team building" seminar. When they are stopped at a roadblock by local police, Mulder decides to investigate, in part to get away from Kinsley and Stonecypher, whose perky nature annoys him. As he and Scully venture into the woods, they are informed by Officer Michele Fazekas that no conclusive evidence has been found to support Louis' report of a shooting. Mulder sees this as a perfect opportunity to ditch the seminar. Later, Mulder explains to Scully that no species native to North America will attack a stronger prey animal when there is a weaker target available, so it makes no sense that an animal would go after Asekoff and ignore his young son.

At the Asekoff residence that night, Bo becomes upset and begins barking. Mrs. Asekoff lets him out, but when she attempts to retrieve him, the dog refuses to budge. She turns around to discover that the door has been shut and locked from the inside. Louis hears his mother's screams and climbs out of bed, but a dark, shadowy figure with red eyes corners him. Louis barely escapes through the dog door and runs into Mulder, informing him that the creature is inside the house. The next morning, Mulder shows Scully some tracks inside the house that appear to be human.

Based on the weight distribution, however, the assailant evidently travels on the balls of its feet rather than from heel to toe. Additionally, that the creature lured Louis' mother out of the house in order to get to him suggests to Mulder that the creatures are paranormal in nature.

Jeff Glaser (Anthony Rapp), a local technician armed with a FLIR device, joins Fazekas, Mulder, and Scully to search the woods for the creature. They soon spot two creatures on the FLIR which travel in separate directions, causing the four to split up. Fazekas is attacked and disappears. Mulder deduces that the creatures may be related to cryptids such as the Mothman. After a brief encounter with the creatures, Glaser takes off running and is swiftly attacked by one of them. Mulder is grabbed by the other creature, though it releases him after Scully manages to wound it with her firearm.

Mulder, wounded in the attack, and Scully spend the night in the woods together. The next morning, Scully falls through a hole in the ground while foraging for food and finds herself in an underground chamber where the bodies of the missing people are being stored. Spotting a pair of red eyes, Scully realizes she is trapped with one of the creatures and does not have her firearm with her. Mulder drops his down to her as the bushes behind him begin to rustle. He jumps into the hole as Scully shoots the creature and kills it. As they examine the dead creature, they notice its almost human-like features and wood-like skin. Nearby, the words ad noctem (Latin for "into darkness") are found carved into a tree trunk. Mulder, Scully, Asekoff, and Fazekas are rescued, but there is no sign of Glaser or the other creature.

Upon leaving the forest, Mulder states that the creatures may, in fact, be evolved versions of the first Spanish conquistadors who had first settled in the forest 450 years before. Although Kinsley finds this idea ridiculous, Mulder believes that centuries of seclusion could be adequate for such drastic adaptations to happen. Afterwards, Mulder realizes that the creatures presume others' presence in their territory as threatening and rushes to the hotel room where Scully is packing her things. After ascertaining that she is finished packing, he firmly urges her to vacate the room, which she does. As Mulder closes the door behind them, the camera then pans under the bed, where a pair of glowing eyes open.