The Last White Rose: The Secret Wars of the Tudors by Desmond Seward
He challenges the way we look at the reigns of Henry VII and Henry VIII, explaining why there were so many Yorkist pretenders and conspiracies, and why the new dynasty had such difficulty establishing itself. King Richard's nephews, the Earl of Warwick and the little known de la Pole brothers, all had the support of dangerous enemies overseas, while England was split when the lowly Perkin Warbeck skillfully impersonated one of the princes in the tower in order to claim the right to the throne. Warwick's surviving sister Margaret also became the desperate focus of hopes that the White Rose would be reborn.
The book also offers a new perspective on why Henry VIII, constantly threatened by treachery, real or imagined, and desperate to secure his power with a male heir, became a tyrant.