1/4 At Fetch Priory a mysterious skull is exerting a deadly influence on those around it.
4/4 The Nucleus has escaped the Doctor's body and grown to human size.
3/4 The Doctor and Leela have been cloned, miniaturised and injected into the Doctor's body.
2/4 As the Doctor's condition worsens, he tells Leela to take him to the Bi-Al Foundation.
1/4 The Doctor is infected by an alien virus and becomes possessed by the will of the Nucleus.