Discworld 31: Monstrous Regiment - Terry Pratchett
Tax included.
It was a sudden strange fancy, and now Polly Perks, in her brother's clothes and with her hair cut off, has joined up to fight for her country, and to search for her lost brother. But who is the enemy? What is she really fighting for? War teaches you a lot, she finds, when it turns out that you have joined the Monstrous Regiment.
