From the Radio Times:

5.50 Colour
Dr Who
starring
Jon Pertwee
The Mutants
A six-part story
by BOB BAKER
and DAVE MARTIN
Part 4: The Doctor and Sondergaard make an amzing discovery in the caves of Solos.  Jo falls into the Marshal's trap.
Title music by RON GRAINER
and the BBC RADIOPHONIC WORKSHOP
Incidental music by TRISTRAM CARY
Script editor TERRANCE DICKS
Designer JEREMY BEAR
Producer BARRY LETTS
Director CHRISTOPHER BARRY