Monstrous Regiment by Terry Pratchett
My rating: 3 of 5 stars
Polly cuts off her hair, names herself Oliver, and joins the army of Borogravia - only to discover that she may not be the only one in her regiment of fresh-faced recruits hiding a secret.
Borogravia is a backward place, with nothing to be proud of but its own excessive pride. This pride has led to endless belligerent warfare, ostensibly under the rule of a Duchess no one has seen in 30 years. Adding to the tiny duchy's woes is the insane god Nuggan decreeing everything an Abomination - from accordion players to cats, redheads, sneezing, and the color blue. Women dressed as men is an especially heinous abomination, you can bet your socks.
But Polly has a plan to save her big brother, so she follows him into the army. She joins up with other new recruits and they soon find themselves playing an important part in the war effort - in spite of their lack of training and supplies.
They are soon dubbed the Monstrous Regiment. The Monstrous Regiment is called such because it contains a Black Ribboner (a teetotaler vampire), a lisping Igor, a lichen-covered troll, and an assortment of humans - including one fervent Joan of Arc who believes she is in spiritual contact with the Duchess herself. (The original phrase Pratchett is playing with belonged to John Knox, and you can read about its origins here.) In fact, most of Polly's fellow recruits prove to be surprisingly feminine, each with his (or her) own reason for joining the army. Heck, even the warhorse is a mare, a fact unnoticed by a near-sighted lieutenant.
For me, this is one of the lesser Discworld novels. It lacks the fizz of Pratchett's best work, especially since the wheels of the plot turn heavily on coincidence and semi-divine intervention. Vimes makes an appearance, always a treat, but Polly, the main character, lacks depth. The supporting characters are much more interesting than she is (though I confess, I do like the implication that she's a natural-born noncommissioned officer).
Still, if you're interested in historical women who passed as men, there are plenty of great stories (from Shakespeare on down). Of course, anyone who likes this book can easily move to any of the other Discworld novels. If you lean towards feminist themes in your fiction, the Witches subseries is a great place to start.
But let me diverge from tradition and recommend a few of the great cross-dressing movies instead of books (though I confess that my list skews to male cross-dressing comedies): First, one I consider to be among the greatest comedies of all time: Some Like It Hot, starring Marilyn Monroe, Jack Lemmon, and Tony Curtis. (Pratchett alludes to it by having one of his many, many cross-dressers assume the nom de guerre of Daphne, which is Lemmon's pseudonym in the film.) And modern drag comedies that aren't Mrs. Doubtfire? First, Tootsie, starring thespian Dustin Hoffman (plus Bill Murray!), then Robin Williams and Nathan Lane in The Birdcage. Thinking of going Shakespearean? Well, I have a soft spot in my heart for She's the Man. Don't judge!