The Viscount at Midnight by Jane Charles

Lady Antonia Kerrigan could speak to animals, and they could speak to her. But nothing could have surprised her more than when she met a very charming wolf, especially since they were believed to be extinct in England. All he asked was for a temporary spell, to make him human for a day. Antonia had not agreed, yet that did not stop her from reviewing her great-grandmother’s spell book to see if it was even possible. Unfortunately, she read the wrong spell, but at least nobody was around who could have been harmed.
When Philip Cardwell, Viscount Chedworth saw Lady Antonia sneak off near midnight, he followed. He wasn’t certain what he’d find, but it wasn’t her sitting in the magical garden reading from a book. As he came from a family of witches, he knew better than to ask, so left her in peace. However, when strange things began happening to his body each midnight, she was the first person he confronted.
Antonia had not even completed the spell, so how could Chedworth be affected? Of course, none of that mattered because if she did not find a way to reverse it by the next full moon…well, she did not even want to contemplate the repercussions. But one thing was certain, no doubt Chedworth would hate her, especially if she did not free him, and he was the only man she had ever loved.