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.
A similar real life incident happened in 1831 off the coast of Sicily when an underwater volcano produced the island of Ferdinandea. As in the book several nations contested for the new land and while they were arguing it eroded back into the sea by 1832.
The trio of Gulli, Gulli, and Betti is an allusion to Wilson, Keppel and Betty.
! colspan="3" | Reading order guide |}