A hopelessly ill-tempered aspiring cop in a crime-infested city is bitten by a vampire, giving him the supernatural powers necessary to defeat the criminals brutally overpowering the local police.

Interesting idea – personally, I’ve seen enough vamps to last me the rest of my life, but everyone else’s appetite for them seems never-ending, so this should do well.

I think the logline is needlessly complicated. It’s always good to suggest a flaw in your character, but it needs to be a strong flaw that relates to what he’s going to do and what he needs to learn through the course of the story. I’m not sure that “hopelessly ill-tempered” does that job.

And what is an ‘aspiring’ cop? Has he applied? Is he in training? Has he been turned down for some unfair reason? This makes quite a big difference to how the story plays out.

Are the criminals vampires too? It feels like they need to be…

I think you could boil this down to something like “When a rookie cop is bitten by a vampire, he becomes the one officer powerful enough to take on the [vampire?] crime syndicate terrorising the city, but [this is where his flaw or weakness plays out, making it possible he’ll lose] “