PC Ventress has bought a building plot and wants to build a new home for him and Mrs. Ventress. He has hired Claude Greengrass and David Stockwell to do the digging at the plot. Suddenly they come across a 500 kg highly explosive leftover from World War II. And Greengrass gets trapped right alongside it. PC Rowan starts to evacuate the village while they wait for the bomb squad to dispose of it. To top it all little Colin Ellis has disappeared and is nowhere to be found when the school children and other villagers have been evacuated. During the search for him the police find a dead body at station master Hutton's house. Suddenly the bomb starts ticking!