The Other Queen by Philippa Gregory

Two women fighting for one man; Two queens competing for dominance Mary Queen of Scots is in flight from rebels in Scotland, and puts her trust in her cousin Elizabeth. But she finds herself imprisoned as the enforced guest of George Talbot and his determined new wife, Bess of Hardwick. The couple welcome the doomed queen, certain that this will bring them nothing but advantage in the competitive world of Tudor England. To their horror they find that their home becomes the epicentre of intrigue against Elizabeth. Even their own loyalty comes under suspicion, as George's hopeless admiration for the beautiful Mary is impossible to hide. The conspiracies come together in the greatest threat that Elizabeth has ever faced. She has no choice but to insturct her spy-master, Cecil, to set the trap to catch her cousin. But even he is caught by the spell of this remarkable young woman, who is prepared to die rather than deny her need for freedom.