Twelve year old orphaned Matty is discontented with life in England where her uncle makes her feel unwanted. She persuades two boys who live next door, Nigel, 13, and Richard, 9, to sail to America on another uncle's sloop. The three set sail and are soon shipwrecked on a small island, which Matty believes to be America. It soon develops that the island, Murra, lies off the Scottish coast and has been evacuated by the population because the Navy is using it as a practice target for jet rockets. The lone inhabitant, Mr. Bull, the church verger, remains to protest each bombardment with a pealing of church bells to sound a funeral knell for the island he loves. When Richard is hurt, Nigel signals for a cease-fire, rescue follows and ensuing publicity causes the navy to desist from further bombardment. Mr. Bull and Matty decide to remain on the island after setting Matty's sloop afloat to give the impression that she set sail again for America and was lost at sea. Pretty improbable, and too violent and unpleasant for most tastes.