Scully and fellow FBI agent Jack Willis stake out a bank after an anonymous informant tips them that a robbery will take place that day. That tip proves correct when Warren Dupre and his wife Lula Phillips stage a hold up. Dupre is ordered to put down his weapon, but instead he shoots Willis in the chest. Scully returns fire and mortally wounds Dupre. At the hospital emergency room, doctors are able to resuscitate the badly injured Willis. Unbeknownst to them, Dupre's consciousness takes possession of the agent's body as he dies beside Willis.

The possessed Willis leaves his hospital room and locates his former body in the morgue. He cuts a finger off the corpse, removing a gold wedding ring. Meanwhile, Scully and Mulder begin their search for the missing Willis. When Mulder learns of the missing ring, he begins to suspect that Willis may be possessed.

Willis locates Lula's brother, Tommy, at a seedy hotel. When Tommy claims not to know Lula's whereabouts, Willis accuses him of tipping off the FBI about the bank robbery. He sees Lula's photograph being broadcast on a local television news program and grows enraged. He shoots and kills Tommy.

Willis reappears at the hotel during the murder investigation. He explains his absence by claiming he wandered from the hotel in a daze and collapsed in the street. Mulder discovers a fresh fingerprint on Tommy's television set-a print left by Willis. That evidence mysteriously disappears soon after being given to Willis.

Willis and Scully respond to a tip about Lula's whereabouts. Scully chases and eventually arrests Lula, but Willis releases her and takes Scully hostage. Dupre's spirit attempts to convince Lula that he now inhabits Willis' body. Those attempts are met with skepticism until Willis reveals intimate details about Lula's life.

Scully tells Dupre's consciousness that Willis is a diabetic and that excess sugar could induce a coma. When a drug store is robbed of insulin and syringes, Mulder suspects that Scully's location must be close by.

Before Willis can inject the insulin, Lula smashes the bottles. She laughs at Willis, revealing that it was she-and not her brother Tommy-who tipped off the FBI about the bank robbery. With Willis now gravely ill, Lula phones FBI headquarters and demands a million dollars ransom for Scully's safe return. Analyzing the phone call for clues, Mulder and his fellow agents narrow the scope of their search.

Willis feigns his death and grabs Lula's gun, pointing it at her. He proclaims his intense love for Lula, then pulls the trigger. FBI agents storm the house, but Willis' body succumbs to diabetic shock and dies. Scully is located and released unharmed.