The White Princess is Elizabeth of York daughter of King Edward IV and wife to Henry VII, the first Tudor king.
Gregory's version of Elizabeth is a far cry from the historical Elizabeth. This story begins after Richard III's fall at Bosworth Field. Here, Elizabeth is Richard's lover and is mourning his death, knowing that she will now have to marry her enemy Henry VII.
Elizabeth endures rape and humiliation, as well as intense scrutiny and suspicion from her husband and his formidable mother Margaret Beaufort. Elizabeth and Henry reach a truce and find love with one another for a brief time.
Gregory's book focuses on the threat of various pretenders to the young Tudor dynasty. The most serious was Perkin Warbeck. In this story, Warbeck appears to be the true Prince Richard, the brother of Elizabeth. It makes a more dramatic, romantic tale if Warbeck is one of the Lost Princes of the Tower.
Ultimately, Elizabeth sacrifices her brother for her sons. Her cousin Margaret Poole does something similar. By not protesting the execution of their brothers, Elizabeth and Margaret may keep her sons from harm. It's dangerous to be a York under Tudor rule.
Gregory does a good job (you won't hear me say that often) showing the suspicion, fear, and paranoia of Henry VII's court. The Tudors may have won the throne at Bosworth Field, but they had to fight to keep it.