It's part of a larger series, but I think there's enough background built into the book that you can understand what's going on with Medraut even if you haven't read the previous Winter Prince. (Short form: he's traumatized from familial abuse and has an exceedingly complex relationship with his legitimate half-siblings, one of whom is present in the book and the other of whom is lost from page 1.) That's really all you need to know. The other really good thing about The Winter Prince is that it shows how much Britain as a whole is impoverished and living in the ruins of the Roman Empire.