The Time Lords take control of the TARDIS and the Doctor and Jo arrive on an Earth Colony in the 25th century, where a ruthless mining company are using a dinosaur-like creature to force the colonists to leave the planet.
Quest roles:
John Scott Martin(Dalek Operator), Nicholas Courtney(Brig. Lethbridge-Stewart), John Ringham(Josiah Blake), Roy Skelton(Daleks (voice)), Pat Gorman(Pilot), Graham Leaman(Time Lord), David Webb(Leeson), Helen Worth(Mary Ashe), John Line(Martin), Peter Forbes-Robertson(Chief Sea Devil), Nicholas Pennell(Winton), Mitzi McKenzie(Nancy), Sheila Grant(Jane Leeson), John Baker(Time Lord)