Something Red by Douglas Nicholas

Something Red
A group of travelers in 13th century England have their journey take a dark turn when they sense something following--something that tears apart animals and people. Everything is seen through the eyes of Hob, the thirteen-year-old boy who considers the travelers his family. The regal silver-haired leader Molly and her granddaughter might be royalty and witches in Ireland. Jack is Molly's lover and a veteran of the crusades. Everyone has a secret. Soon, the travelers meet a band of gentrified pilgrims escorting an elderly aristocratic lady, and they all become allies against the beast that follows them.
The tale is filled with rich historical detail, intriguing characters, and a mystery that descends into horror when they seek asylum at a castle (plus those delicious secrets some of the characters hide). The ending is a terrifying revelation.