It then moves on to an image of the stream running through the village of Cwmgiedd (half a mile from Ystradgynlais in west Wales), and an eight-minute opening sequence interspersed with images and sounds of everyday life in a community in the Upper Swansea Valley; men are shown working at the colliery, women engaged in domestic tasks in their homes and the inhabitants singing in the Methodist chapel.
Little is shown of the occupation itself, its violence being implied by a soundtrack of marching boots, gunfire and harshly amplified orders and directives, in the sound-as-narrative technique Jennings had previously developed in Listen to Britain.
The identity of the community is eroded, with the Welsh language being suppressed and no longer permitted as the teaching medium in the school, and trade union activity being made illegal.
The catalyst for the systematic obliteration of Cwmgiedd in a reprisal is intended to parallel the consequence of the actual murder of the leading Nazi Reinhard Heydrich the previous year.
The murder of Reinhard Heydrich, whose assassination (Operation Anthropoid) by British-trained Czech agents in Prague led to the actual Lidice massacre.
The film recreates events in Lidice but transports them to a South Wales mining community to indicate that if the German invasion of Britain had been successful in 1940, then the kind of atrocities currently being perpetrated in German-occupied Europe would just as likely be happening contemporaneously in the UK; also as a reminder to the British people of what they were fighting against.
Jennings had decided that no professional actors would be brought in, and his entire cast consisted of untrained local people, although he was careful to ensure that nobody appeared on screen without giving their permission and that anyone who felt uneasy or uncomfortable about being filmed was excluded from shots.
Contemporary opinion places it among the products of Jennings' most fruitful period as a director alongside Listen to Britain, Fires Were Started and A Diary for Timothy.