While attending to a dying man in an ambulance which is hit by a truck, Leonard Betts is thrown out and his decapitated body is found nearby. The interesting thing is that Bett's body is now missing from the hospital morgue.

When Mulder and Scully view security video footage of the incident they see a man walking out of the hospital with a strange distortion round the head. While going through a bio-disposal unit, they find Betts missing head but his body's location is still a mystery. When Scully performs an autopsy on the head it's eyes and mouth suddenly open.

A tissue sample from his head suggests that it was filled with cancer cells which leads Mulder to believe that Betts possesses the ability to regenerate himself and grow new body parts. They find out Betts' real name is Albert Tanner but when they interview his wife, she tells the agents that he died in a car crash 6 years earlier.

Meanwhile, another ambulance is transporting a patient when an Emergency Medical Technician named Michelle Wilkes hears Betts' voice over the ambulance radio and instantly recognizes it. Wilkes locates Betts at a hospital where he suddenly injects her with a lethal substance. A security guard captures and handcuffs Betts but he escapes by ripping off his thumb and sliding out. When M & S search Betts' car they come across bags filled with human tumours and Mulder concludes that Betts must be digesting them to keep his special powers.

But his powers also enable him to spot people with tumours inside them and he kills a man outside a bar. Later, Betts actually gives birth to a clone of himself! Back at Mrs. Tanner's home, the agents find a locker key which they find opens the door to a locker which contains the body of the man Betts killed, his left lung ripped out. Out of the blue, Betts attempts to run down the agents but they dodge out of the way and open fire which sets the car on flames incinerating Betts.

Mulder finds that Betts must have eaten the man's lung. When they examine the casket of the man Mrs. Tanner claims to have been killed in the car crash, they find another Betts inside it. This means that the real Betts is still alive.

While searching through Mrs. Tanner's home, an ambulance arrives and when they jump inside it they find Mrs. Tanner with a surgical cut on her chest. At the hospital, Betts jumps aboard the ambulance leaving Scully alone with the murderer. He tells Scully that she has 'something I need' before Scully kills Betts with defibrillation pads. At night, Scully wakes up with blood on her pillow having come from her nose. She realizes what Betts' words meant....