The book opens on Thanksgiving evening, 10 years after the events of "A Wind in the Door". Meg is now married to Calvin and is expecting their first child. Calvin has become a scientist and is in Britain at a conference; Calvin's mother Branwen Maddox O’Keefe joins Meg's family for Thanksgiving dinner. When they receive the news of impending nuclear war caused by the dictator "Mad Dog Branzillo", Mrs. O'Keefe lays a charge on Charles of Patrick's Rune, a rhyming prayer of protection inherited from her Irish grandmother.