Searching for a missing girl, two detectives become trapped in a manor filled with a secret society of vampires – and must get out before eaten alive.

I changed it again so the INTENTION is stronger.

INTENTION: Find the girl.

OBSTACLES: Vampires. Everywhere.

I think you're right with the original logline. They wouldn't just go to a vampire's house.

That's a twist. He kills one of the detectives (hopefully a big name actor. someone you wouldn't expect.)

He then skins him. Cooks him. Serves him to his friend - who is drugged or incapacitated.

The villain is a Southern Gentleman - he is wining and dining him first. Then he'll kill him.

It's like with IT - why doesn't the clown just kill them? Well, he's feeding off their fear. I might lean into a weird sexual thing. Maybe this vampire aristocrat literally gets off on seeing this guy's fear/dread, etc.

Have you seen the end of BONE TOMAHAWK? If I can replicate that ending ha.

Getting there. Why doesn't the vampire just kill them? I hate it in films when the bad guy doesn't just kill the good guys when he has the chance.

Maybe the detectives sneak into his manor instead... undetected. They come and question him but they (in a nice flip on a standard vampire trope) they decline the invitation to come inside. The audience gets to see this charming southern gent vampire but not arouse so much suspicion that would result in instant death.