Every May Day, the Obby Oss dances through the streets of Padstow. Thirza and her brothers join in, with the whole village. But Thirza never sees her father on May Day. In this particular year, the men sail off to fight the King's war against the French. The town of Padstow is left to the women and children. Then one day Thirza sees a French warship coming to attack Padstow. Turnning to warn the others, she bumps into the frightening figure of Aunt Ursula Birdhood. Aunt Ursula tells the boys to grab musical instruments and the girls and women to put on their red Sunday cloaks. She puts on the Obby Oss skin and makes Thirza dance in front of her. Together they save the village and Thirza learns the secret of what her father does on May Day.