The Doctor and UNIT investigate a deadly infection lurking underneath the Welsh mining town of Llanfairfach. It's an adventure that will change Jo Grant's life forever...
Jon Pertwee
as The Doctor
Katy Manning
as Jo Grant
Nicholas Courtney
as Brigadier Lethbridge-Stewart
John Levene
as Sergeant Benton
Richard Franklin
as Captain Mike Yates
Stewart Bevan
as Cliff Jones
Jerome Willis
as Stevens
Tony Adams
as Elgin
Ben Howard
as Hinks
Mostyn Evans
as Dai Evans
Talfryn Thomas
as Dave
Roy Evans
as Bert
