What do you get when you cross a vampire, a troll, Igor, a collection of misfits, and a young woman who shoves a pair of socks down her pants to join the army? The answer's simple. You have Monstrous Regiment, the characteristically charming novel by Terry Pratchett.
Polly becomes Private Oliver Perks, who is on a quest to find her older brother, who's recently MIA in one of the innumerable wars the tiny nation of Borogravia has a habit of starting with its neighbors. This peevish tendency has all but expended Borogravia's ranks of cannon fodder. Whether Sergeant Jackrum knows her secret or not, he can't afford to be choosy, as Perks and her/his comrades are among the last able-bodied recruits left in Borogravia. This collection of misfits includes the aforementioned vampire (reformed and off the blood, thank you), troll, and macabre Igor, who is only too happy to sew you a new leg if you aren't too particular about previous ownership. Off to war, Polly/Oliver learns that having a pair of, um, socks is a good way to open up doors in this man's army.