The Princess, the Crone, and the Dung-cart Knight (Squire's Tales, 6)

Ever since that tragic night when her mother and guardian were murdered, thirteen-year-old Sarah has been living on her own and searching for the knight who was responsible. Her quest for revenge leads to an even greater adventure when she witnesses Queen Guinevere being kidnapped. Soon Sarah finds herself accompanying Sir Gawain and Squire Terence on a remarkable journey to rescue the Queen. In their travels they meet, among others, a mystery knight traveling incognito in a dung cart, a faery who becomes Sarah’s first friend in a long time, a reclusive monk who plans to spend the rest of his life building a tomb for Sir Lancelot, and a princess who might have a little more gumption than she appears to.
As the plot thickens, Sarah finds out more about the people she’s met and befriended, as well as about herself. She begins to learn the true consequences of vengeance and what it really means to be a princess.