Time’s Fool by Karen Chance

Long before Dorina Basarab was a respected member of the Vampire Senate, she was an outcast known as a dhampir. Half human, half vampire, all pariah, she scraped out a living catching monsters even more terrifying than herself. But perhaps the greatest foe she ever faced was also the most unusual—and the most dangerous.
Kit Marlowe wasn’t always a senator, either. Once, he was a master vampire with none of the wealth, family or experience that the rank should have afforded him. He had been Pushed, or forced into the position through a ritual that had risked his life, because his master desperately needed an operative who knew Elizabethan England. Leaving Kit two years into his undead life and facing a country about to go up like a powder keg.
Gillian Urswick was a witch torn between two men: the one she loved and the one she’d lost. But sorting out her heart required solving a mystery that involved the past and the present, as well as any hope she might have for a future.

Together, Dorina, Kit, Gillian and the mysterious vampire Mircea, end up on a mission that will either save the world, or help destroy it.