It is important, when killing a nun, to ensure that you bring an army of sufficient size. So begins Red Sister by Mark Lawrence. Nona Grey lives on an ice world where humanity huddles around the equator and jealously guards its remaining resources. Nona is a slave sentenced to hang for murdering a nobleman. She's ten years old. Abbess Glass of the Sweet Mercy Convent rescues her and Nona becomes a novice. There are ultimately three paths the nuns can choose, but for ten years Nona and the other novices learn the basics of combat, magic, and prayer. Political fallout from Nona's rescue, assassination attempts, and an ancient prophecy combine to add intrigue to a tale of friendship, growing up, and kick ass nuns.