The Heirloom — Mary Balogh

A bewitching sapphire engagement ring leads a skittish groom to Regency Wales -- where he learns there is no love like the present...

The Heirloom by Mary Balogh
In order to celebrate his engagement, John Chandler drives his girlfriend from London to a remotely situated hotel in West Wales, once the home of his ancestors. However, when John produces her ring, an old family heirloom, and fits it on her finger, he finds himself catapulted back in time to become the John Chandler of Regency England, newly arrived at the house with his new wife -- and dying of consumption.