Miniaturised clones of the Doctor and Leela are injected into his brain. But they must now fight the virus on its own level. And its servants are closing in around them.
Quest roles:
John Scott Martin(Nucleus), Pat Gorman(Pilot), Michael Sheard(Laurence Scarman), Frederick Jaeger(Professor Marius), Roy Herrick(Parsons), Elizabeth Norman(Marius' Nurse), Jim McManus(Opthalmologist), Roderick Smith(Cruikshank)