Jingo is the 21st Discworld novel by Terry Pratchett, and one in the "Guards" subseries.
It all begins when an island suddenly appears in the sea between Ankh-Morpork and Klatch. Both states naturally lay claim to this island, and the conflict escalates.
The Klatchian Prince Khufurah has been invited to Ankh-Morpork, and when someone tries to assassinate him on a parade, Commander Vimes finds himself with too many clues. The Prince is taken to the Klatchian embassy, which later on is set on fire. His servant or bodyguard, 71-hour Ahmed, with a face that looks like it can't be innocent of anything, then leaves the city by ship. Lance-Constable Angua sneaks onto the ship in her second shape, but doesn't return.
The Patrician, Lord Vetinari, steps down from office when the war is drawing nearer, and the aristocrat Lord Rust takes over. Vetinari is then seen with Leonard of Quirm, who has invented a Going-Under-Water-Safely Device. With the more or less voluntary aid of Corporal Nobbs and Sergeant Colon they start to paddle off towards the new island and Klatch.
Vimes and most of the Watch then set out after 71-hour Ahmed and Angua in another ship, surprising the Klatchians and Lord Rust both with an early start of the war.
Once in Klatch, Nobby gets to explore his feminine side, the Patrician shows remarkable skills at circus arts, and Captain Carrot does wonders with a football.
This is one of the slightly more serious books in the series, while at the same time being funny enough to be potentially embarrassing to read in public areas. It seems that Pratchett by now considers his characters to be established enough, and most of them don't develop very much in this book. The exception being the Patrician, who gets a lot more attention here than in the earlier books.
"It was so much easier to blame it on Them. It was bleakly depressing to think that They were Us. If it was Them, then nothing was anyone's fault. If it was us, what did that make Me? After all, I'm one of Us. I must be. I've certainly never thought of myself as one of Them. No one ever thinks of themselves as one of Them. We're always one of Us. It's Them that do the bad things."
For more information, see also the L-Space Web at http://www.ie.lspace.org/ . Quote from Terry Pratchett: Jingo, Corgi books, 1997