The episode begins with an ambulance rushing to a hospital. Paramedic Leonard Betts is working on the patient, he knows the man is dying of cancer… But how does he know? The ambulance crashes and Leonard Betts is thrown from the vehicle. He is found by his driver, lying on the floor. Dead, Decapitated.
Taken to the Morgue, Leonard is put away. His head and body separated. Night falls and the young man watching the morgue is attacked, by what looks like Leonard's Headless body. All the evidence, videotape and Leonard's missing body point towards the dead paramedic being responsible. Searching through medical waste Mulder and Scully find Leonard Betts' Head, but no body. As Scully works on the head, it begins to move. Postmortem galvanic response? The mouth and eyes open. Mulder enters Leonard Betts' apartment. Searching it alone he heads for the bathroom. What looks like blood on the floor and in the bath turns out to be Povidone Iodine, along with the stolen uniform from the man at the morgue. As Mulder leaves, the bath begins to bubble, slowly a head appears. Leonard's Betts rises from the Iodine
Taking a sample from his brain, the agents look under the microscope, looking for a clue in to Leonard Betts' life. They find his brain riddled with cancer. No man could possible live with this. Mulder and Scully take the sample and have it digitally analyzed. They find energy in the scan, emanating from Leonard' s head. Mulder theorizes that the cancer in his brain was his way of life, not an illness. His 'chi' is to live with it.
A phone call confirms that Leonard Betts had an alter ego – Albert Tanner. Albert has a living relative, his mother. Visiting her they find a picture matching both people. When they mention her son is dead. She seems shocked. Her son died in an automobile accident six years ago.
Leonard's partner tracks him down, she follows him to a quiet grass area, in shock she can't believe what's happening. Leonard moves in for a hug, comforting his friend, taking advantage he injects her with Potassium Chloride. As she slowly dies, a security guard sees them. He gives chase as Leonard runs through parked cars. Finally getting caught and handcuffed to a car. It looks as if there no way to escape. Leonard pulls of his own thumb allowing him to escape. Now easily slipping through the cuff, he disappears.
Mulder theorizes Leonard Betts is an evolutionary leap. Something more advanced than they could know. They discover that Leonard Betts doesn't only have cancer, but he also needs it for sustenance. The car Leonard has been driving is tracked. It's Albert Tanner's Mum's car. They get a warrant and search her house. 'God put him here for a purpose, God means for him to stay' is her reasoning for Leonard doing what he does.
In a bar, Leonard watches a man closely, as the man leaves, Leonard follows, staying close. The man stops at his car, Leonard reveals a knife "I'm sorry, but you have something I need".
Alone, Leonard screams. A new head pushes out of his mouth, like he is shedding his skin. Mulder and Scully pull up to the garage and see blood seeping out from underneath the door, they draw there weapons and open the door, the man Leonard followed falls out, and Leonard Betts screeches away in a car. Moving out of the way the agents turn and shoot. Two shots hit the car and it explodes.
In the Morgue, the agents stand between two identical bodies. How could this be? Could they be twins? Leonard is sat, regenerating in his mum's bath, His mum washing him with the iodine substance. Mulder and Scully watch as an ambulance screeches up out side the mum's house, they run in, searching it. Leonard removes his mum's cancer and leads her to her bed.
Scully goes with the mum, as Mulder searches the block. As they talk on the phone Scully feels a liquid running down her head. She examines it, it's Iodine. Leonard traps Scully in the ambulance. Scully is shocked when Leonard tells her 'I'm sorry but you've got something I need'. A fight ensues. Scully finally wins, using the Defibrillator on him. He dies, his mum survives, thanks to Leonard's careful dressing of the wound. Scully seems distant as she sits in the car, worried that Leonard Betts had identified something inside her. A nose bleed leaves a cliff hanger at the end, as Scully's worries seem to come to fruition.