Rosemary & Iron (The Eastern Quarter's Mana, #1) by Dorian Valentine

When a ritual to restore Mana goes wrong and sends him into the distant past, Célestin Edevane seeks the help of a strange man inhabiting an even stranger estate in order to prevent the calamity that destroyed Mana. Faced with a fascinating world unlike his own, filled with vampires, fae, witches and old gods and an unexpected love affair...will he even want to return to his time?