The Guardian Duke, Forgotten Castles Series Book 1

"The Guardian Duke" is award-winning novelist Jamie Carie's most exciting story yet, a uniquely arranged Regency-era romantic adventure where hero and heroine know each other through written letters but have yet to meet.
Gabriel, the Duke of St. Easton, is ordered by the King to take guardianship over Lady Alexandria Featherstone whose parents are presumed dead after failing to return from a high profile treasure hunt. But Alexandria ignores this royal reassignment, believing her parents are still alive and duly following clues that may lead to their whereabouts. Gabriel, pressured by what are actually the King's ulterior motives, pursues her across windswept England and the rolling green hills of Ireland but is always one step behind.
When they do meet, the search for earthly treasure will pale in comparison to what God has planned for both of them.