S3E18 · Teso dos Bichos

At an archaeological dig in the Ecuadorian highlands, two archaeologists, Dr. Bilac and Dr. Roosevelt, get into an argument over the removal of a burial urn that contains the remains of an Amaru, or female shaman. Roosevelt argues the urn must be taken from the site and preserved in a museum, much to the chagrin of Bilac and the tribespeople present, who believe disturbing the Amaru will invoke a curse. Later, a native shaman distributes Yaje to the local villagers and Bilac. During this ritual, a jaguar spirit kills Roosevelt in his tent.

Later, in Boston, Fox Mulder and Dana Scully investigate the disappearance of Dr. Craig Horning, an archaeologist working at the local Museum of Natural History, after a security guard discovers a large amount of blood in Horning's lab. They interview both the curator, Dr. Lewton, and graduate student Mona Wustner. They also visit a reclusive Bilac. After closing, Lewton is killed by the jaguar spirit after his car fails to start. During an investigation of the crime scene, Scully comes across rat corpses in the engine compartment of Lewton's vehicle. Mona denies that anything unusual has happened in the museum, but when she visits Bilac later, she discovers he has been abusing Yaje and is approaching a psychotic state.

Mulder and a group of police search for Lewton's remains in some woods near the museum. Scully sees blood dripping on Mulder's face from above and, upon looking up, they see a portion of Lewton's intestine hanging from a tree. Scully, about to perform an autopsy on the intestine, is interrupted by a panicked Mona's phone call. Mona reports that Bilac has been consuming Yaje. Alone at the museum, she hears noises from a restroom and, upon opening a toilet lid, sees rats forcing their way out of the sewer. When the two agents arrive, they discover Bilac crying beside one of the toilets, saying that Mona is dead.

Mulder and Scully place Bilac in the custody of two local policemen, but he escapes from the room in which he is being held without exiting through the only door. Mulder notices a large drag mark through the dust on the floor, discovering a hatch leading to the museum's old steam tunnels. While exploring the tunnels, the agents find the remains of the victims and are attacked by hundreds of feral cats. Discovering the hatch through which Bilac was dragged, they pull out his mutilitated body and escape, closing the hatch on the pursuing cats. A short while later, animal control informs Mulder and Scully that they discovered no signs of cats in the steam tunnels.

The episode closes with Mulder musing in his journal. He writes that he suspects the animal attacks were associated with the burial urn that had been removed against the wishes of the Ecuadorian tribespeople. As the urn is returned to the burial grounds, the local shaman watches the urn's reburial with jaguar-like eyes.