Earth, South Wales. The suspicious death of a miner at the inactive local pit owned by the mysterious Global Chemicals brings UNIT to sleepy Llanfairfach. There, a local green group - the Wholeweal Community under the leadership of the brilliant Professor Jones - are not convinced of Global's innocence in the affair. Could the waste products from their revolutionary new oil refining process be at fault? Jones is convinced but the Doctor is not so sure and a dangerous expedition down the mine confirms his fears.

For there, thosands of giant maggots lie gestating - a dangerously unknown terror waiting to be unleashed upon the world. But by whom? Just who is the power behind Global Chemicals? Who or what is the Boss? And what are his/its plans for the Earth? The Doctor, Jo and the Brigadier must move quickly to find the answers, for the death toll is already rising and the gestation period of the maggots down the mine is coming to an end

This story originally broadcast: 19/05/73

Writer - Robert Sloman, Barry Letts (uncredited) Director - Michael Briant Producer - Barry Letts