The Daleks draft the Second Doctor into distilling the Human Factor. Once implanted, it will make the Dalek race invincible. Jamie's faith in the Doctor is stretched to the limit as the Doctor appears to be collaborating with the Daleks. The Doctor has a few tricks up his sleeve, but then again so might the Daleks.

• BBC
• Patrick Troughton
• Frazer Hines
• Deborah Watling
• John Bailey
• Marius Goring
• Brigit Forsyth
• Geoffrey Colville
• Griffith Davies