Geoffrey Jones, M.P. and sometime architect, is convinced that the Russians are about to launch a nuclear strike against England. He builds a bomb shelter equipped with everything he, his wife, and his wife's old mother will need to last out such a strike. They plan to try the thing out for a three week experiment when, inadvertently, they are trapped inside with the mother, the telephone installer and an Indian milkman. They try to make the best of the situation when who should enter through a side hatch but their next door neighbors who, ever striving to keep up with the Joneses, have now kept down with them by building their own abutting shelter. By a strange set of circumstances the neighbors are also trapped and neither neighbor wants to admit this to the other. Hilarious complications ensue until everyone gets out.