In the mid 1950s, Liverpool demands more water for its industries. The Tryweryn valley near Bala in North Wales is chosen for a new reservoir. But a community will be drowned in the process and residents lose their homes and livelihoods. Debates in Parliament and protest marches achieve nothing. Can direct action be taken? Smallholder Rhydian Williams is persuaded that it can and devises a plot to stop the reservoir dam being built. DI Terry Richards of Special Branch is sent from Cardiff to find out what is going on and to take action as needed. With the help of local police officers Sergeant Eddie Jenkins and WPC Rhian Davies, he intervenes but with fatal consequences for those involved.