Monstrous Regiment by Terry Pratchett
Polly's brother (her sweet, innocent, artistic brother) left their family's tavern to fight in Borogravia's endless war. When his letters suddenly stop, she wants to go looking for him, but women aren't allowed in the Borogravian army. Undeterred, she chops off her hair, stuffs some socks down her trousers, and joins up anyway, disguised as "Oliver." She's always been told that the Borogravian army is the Discworld's finest, and that they're winning the war, but that's hard to believe when she sees her brothers-in-arms: all oddballs and misfits, untrained and ill-equipped. As they charge to the battlefront, running on blind faith and stubbornness (and coffee for their resident vampire), getting caught up in nonstop hijinks along the way, who knows what unexpected truths they might discover-- about the war, and about their country, and even about each other.
This novel takes place in Pratchett's Discworld series, but like most Discworld books, it can easily be read out of series order, or as a standalone. As is typical of the series, it swerves between socio-political critique and bawdy comedy in the same breath. The cast of characters is odd, but compelling. It's hard not to root for them. Polly makes for a clever and level-headed lead, and the twists of the plot, and Pratchett's masterful turns of phrase, will keep you gasping and laughing for the whole book. I recommend the audio version, where the narrator does an amazing job with the fantasy pronunciations and character accents.
--Caroline, Reference Librarian