The book deals with a war between Ankh-Morpork and Klatch over the island of Leshp, which unexpectedly rises from the sea after centuries of submersion. When Samuel Vimes uncovers signs of a conspiracy, he and the members of the City Watch, with the assistance of the mysterious 71-Hour Ahmed, try to bring a stop to the oncoming conflict. Meanwhile, Fred Colon and Nobby Nobbs find themselves drafted by The Patrician into using an experimental Going-Under-the-Water-Safely Device to travel to Klatch and do some reconnaissance.