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... 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... 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... 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...