S6E16 · Alpha

On a freighter in the South Pacific, two Chinese men inspect a crate with an animal inside. When the ship reaches the Port of Los Angeles, the authorities find the two men dead of vicious bite wounds inside the locked crate and the animal missing. After Fox Mulder (David Duchovny) receives word of the attack from the mysterious Karin Berquist (Melinda Culea), an expert on canine behavior, he and Dana Scully (Gillian Anderson) go to investigate the incident on the ship with the help of San Pedro officer Jeffrey Cahn (Thomas F. Duffy). Meanwhile, in Bellflower, California, a man hears his dog barking in the backyard and lets it in the house. He hears another dog in his backyard and chases it off. After returning to his house he finds his pet dead and is attacked by the other dog, a wolflike creature with glowing red eyes.

Mulder and Scully arrive at the port and talk to the man who imported the dog, Dr. Ian Detweiler (Andrew Robinson), a cryptozoologist. Detweiler says the dog is a Wanshang dhole, a species thought to be extinct. The two agents soon receive news of the other attack and, after investigating, Mulder believes the dhole has near-human intelligence. Mulder and Scully visit Berquist, who tells them that the species they are looking for is extinct. Meanwhile, a dog catcher is chasing a stray through a warehouse when a man enters the building. He promptly transforms into the murderous dhole and attacks the dog catcher. Mulder and Scully arrive at the scene, followed by Berquist, who finds a paw print with five toes.

Later that night, Detweiler arrives at a vet's office to get tranquilizers. The vet goes to the office's kennel area and is attacked by the dhole, but is able to escape and lock the kennel door behind him. The dog catchers arrive and open fire, but the fallen animal turns out to be a Saint Bernard brought there by its owner. While the vet tries to operate on the hurt Saint Bernard, Scully arrives and hears screams coming from the kennels, where she discovers that the vet has been attacked. After Scully leaves, the wounded Saint Bernard on the operating table transforms into the dhole, revealing that it can mimic any shape.

Scully begins to question Berquist's motives, noting that she was the reason Mulder decided to look into this investigation. Mulder, however, begins to suspect Detweiler after learning that he had been at the vet's office; Mulder believes that he is the dhole and is tranquilizing himself in an attempt to stop killing. Mulder asks Cahn to confront Detweiler, but Cahn is attacked and severely injured by the dhole and placed in the hospital. Mulder visits Berquist and says he thinks she has not been honest with him. Berquist reveals that she first suspected Detweiler when she saw him. She also says that he will try to finish off Cahn. Mulder worriedly tells Scully, who remains skeptical.

Later, Berquist hears something in the woods while locking one of the outside kennels at her home. She goes upstairs to retrieve a tranquilizer gun, but when Detweiler, in the guise of the dhole, enters her bedroom to attack her, she sets the gun aside and challenges the dhole. He attacks, causing both of them to fall out of the window behind her. Mulder and Scully arrive and find Detweiler's and Berquist's bodies, the former impaled on a fence spike. Back at the office, Mulder receives a package from Berquist; it is her "I Want to Believe" poster, a replacement for the one he lost in the fire and last seen hanging on her home office wall.