"Field Trip" is the twenty-first episode of the sixth season of the science fiction television series The X-Files. The episode first aired in the United States and Canada on May 9, 1999 on the Fox Network, and subsequently aired in the United Kingdom on Sky1. Frank Spotnitz came up with the story and John Shiban and Vince Gilligan wrote the teleplay. The episode was directed by Kim Manners.
In the episode, a mystery involving two skeletons leads the agents on a journey in which nothing is quite as it seems. The episode was generally well-received by fans and critics alike. The episode is a monster-of-the-week (standalone) episode.
The episode opens with Wallace and Angela Schiff returning home after a day out hiking in the fields of North Carolina. Angela appears to be exhausted after spending most of the day chasing after her overeager husband and is starting to get a headache. Whilst taking a shower she thinks she is hallucinating and sees images of a yellow gooey substance running down the walls in the shower but shakes it off. Angela and Wallace head off to bed in one other's arms but as the camera pans out the scene shifts to their skeletal remains in the same position in the middle of a field.
Mulder is filling in Scully about the discovery of the remains at a well-known site of strange unexplained phenomena but Scully seems keen as ever to find a more rational explanation. After showing her images of the bones and the fact they were only a few days old Scully concludes it looks like a ritualistic killing and that the bones were stripped of the flesh by boiling with/or acid. However, they head off to examine the remains themselves.
The coroner is just about to send the remains away for burial when the agents arrive to view them. After closer examination they find a strange yellow goo covering the underside of the skeletons which was missed in the original examination. Mulder heads out to the scene of the discovery while Scully stays to perform more testing on the remains.
As Mulder arrives in the fields, he inadvertently drives over a patch of mushrooms with his car which seem to release a cloud of smoke. As he exits the vehicle and takes a look around he spots what he thinks is Wallace running away and takes chase, eventually following him down a cave. Inside the cave, Mulder finds that the way he came in seems to have been replaced with solid rock. He catches up with Wallace in the cave he discovers that Wallace thinks he and his wife Angela have been abducted by aliens and covered up their disappearance with the false skeletons. Meanwhile, Scully has discovered that the yellow goo mainly consists of organic material found in digestive juices but this seems to emanate from a plant rather than an animal. Unable to reach Mulder on the phone, she heads off to find him.
Arriving at the field, Scully starts to look for Mulder and accidentally steps on some more of the mushrooms that Mulder flattened earlier. Starting to follow his tracks, Scully finds they lead up to the cave and apparently lead inside.
Mulder and Wallace are now talking when a bright light appears in the tunnel entrance. Wallace is scared that it is the aliens returning but Mulder heads up to take a look and finds Angela has returned from her abduction. After describing the text book story of the tests that have been performed as well as locating an implant, Mulder starts to believe their story. Once again, the bright light from the tunnel entrance begins to shine and Mulder heads up to investigate.
The scene fades to Mulder's front door as Scully arrives. Mulder answers and checks she is on her own before letting her in. Inside are Wallace and Angela. Mulder explains how they got there. Scully still doesn't believe the alien abduction story until Mulder shows her into his bedroom and hiding behind the boxes in the dark is an alien creature. Scully is astonished and quickly apologizes to Mulder for ever doubting him. However, Mulder starts to doubt his surroundings and his disbelief in what is going on begins to increase. As he washes his face with water he starts to see the yellow goo Angela saw earlier but quickly shakes it off as a hallucination. But, as he discusses the situation with Scully, his apartments seems to dissolve and everyone seems to melt into the yellow goo. Mulder awakens in the cave he followed Wallace into earlier, covered in the yellow goo, being digested alive.
Outside in the field, Scully and the coroner happen across more of the yellow goo. The coroner also spots footsteps leading out of the cave which Scully insists weren't there earlier. However, as the coroner follows them, he finds Mulder's skeletal remains lying on the floor.
At the coroner's office, Scully is identifying Mulder's remains from his dental records but finds no evidence of the goo on the skeleton. The coroner then informs Scully that he believes that this is a ritualistic killing with boiling of the bones in an acid to remove the flesh, the theory Scully had originally believed to explain the remains of Angela and Wallace.
Back at the FBI, Scully is reporting back to Skinner about her report and her findings of the deaths of Mulder and the Schiffs. Skinner seems to agree with Scully's report but Scully is herself doubting her own findings and is not convinced by her own theories that everyone seems to be agreeing with.
Mulder's wake is in progress at his apartment. Notably, Skinner and the Lone Gunmen are in attendance along with several others. The Gunmen tell Scully they looked at her report and totally agree with her findings which Scully finds unbelievable. There is a knock at the door and Scully answers but finds Mulder standing in the doorway. The rest of the wake congregation has disappeared. As Mulder and Scully discuss what has happened, they both begin to realize that they are both still in the cave being digested by the goo and that the mushrooms they broke caused an LSD-type trip causing them to become comatose whilst the organism began digesting them. As the realization occurs, they both awaken, deep in the cave and Mulder fights his way out of the ground dragging Scully behind him to safety.
In Skinner's office, where Mulder and Scully report on their findings, that an organism spreading many miles underground lures its prey into being consumed by inducing a hallucinogenic trip whilst it digests them. Skinner notes that this it is rare that their reports agree on the same conclusion. However, Mulder begins to doubt that they're free at all, asking Scully to name any sort of drug that causes its effects to halt once the user knows they are hallucinating, and observing that they have no apparent flesh injuries despite being exposed to the goo's hydrochloric acid. Scully is in disbelief until Mulder proves his point by shooting Skinner in the chest; the yellow goo oozes out of the bullet wounds.
Once again, their surroundings melt away as they awaken underground again in the cave. Mulder manages to stick his hand through the earth ceiling as Skinner and a team of rescue staff with masks on manage to locate them and drag them out and haul them to the safety of an ambulance. Scully murmurs "Mushroom," to Skinner, with Skinner replying that they already "found it." Once inside the ambulance, Mulder and Scully weakly hold hands.
One of my favorite episodes ever!