In the near future, zombies and werewolves and vampires are real (and licensed by the government). But when a paranormal creature goes rogue, regular law enforcement isn't equipped to deal with the problem. So the government creates a special law enforcement agency to deal with them when they get out of line.
The trick is that you can't be "trained" to detect vampires and werewolves, it's an innate ability. So people from all walks of life become Special U.S. Marshals under a Presidential Order.
One man, a former Texas Sheriff, is the only law enforcement professional in the new Special Marshals. He has the best vampire arrest record in the country.
And he's just been given a new partner. And she's a vampire.
See? It's a TV series. And because the monster of the week can be virtually any paranormal creature, it can be as romantic or icky as you want. Some of the monsters will be good. Some will be informants. It'll be like Law & Order only with vampires.