A Knight in Shining Armor by Jude Deveraux
Abandoned by her lover, thoroughly modern Dougless Montgomery finds herself alone and brokenhearted in an old English church. She never dreamed that a love more powerful than time awaited her there... until Nicholas Stafford, Earl of Thornwyck, a sixteenth-century knight, appeared. Drawn to him by a bond so sudden and compelling that it defied reason, Dougless knew that Nicholas was nothing less than a miracle: a man who would not seek to change her, who found her perfect just as she was. But she could not know how strong were the chains that tied them to the past - or the grand adventure that lay before them.