In the year 2019 a plague has turned 95% of the population into vampires. Humans that have not "assimilated" are either farmed for their blood or in hiding. This isn't great for the vamps as human blood is dwindling and they are faced with a grim future. Early in the film we see that vampires who do not get an adequate blood supply become these freaky, wild, winged creatures called subsiders, that will go after anything - other vamps included.
The way the world has adapted to fit vampire life is pretty cool. Things are slick with that futuristic trend of having everyone of affluence dress like it's 1940-something. There are blood coffee stands on street corners. The vampire neighborhoods have a PA system announcing when dawn is approaching. They have outfitted their cars with a switch to go to "day driving" where the windows turn black and cameras mounted on the car shows a 360 view. A lot of them smoke cigarettes, because hey! it's not going to kill you!
Our main guy is Edward (played by Ethan Hawke in his most pinchy face), a vampire that works at Bromley Marks, a big conglomerate vampire pharmaceutical company.
Those pharmaceutical companies always come out on top, huh? Anyway, Ed is the head hematologist, and he is working desperately to try to find a synthetic blood substitute that will solve the lack of blood dilemma. His idea is that once a substitute is found, the humans can be saved. He's a bit naive, our Ed. He refuses to feed on human blood - preferring animals instead. Something his brother Frankie, a human-hunting military soldier, is quick to make fun of him for.
As the blood rationing get worse, things start to go a bit crazy in downtown vampire-ville. Then Ed meets up with some humans who are working on a "cure." Turns out their leader, Willem Dafoe, used to be a vampire. Then this freak accident happened to him and his heart started beating again and lo and behold, he could now go outside at noon without frying. Of course, Ed is all over this shit because he, again naively, thinks that if they can find a cure all the vamps are going to get in line to be humanized. So he joins up with the humans to try to help them recreate the freak accident.
Then after all of this thinking - the end is a huge blood bath! But again, not in a good way! They tried to create this operatic scene with flying bodies and tons of blood and guts and it just felt so weirdly staged. I don't know, it didn't work for me. I'm not saying don't see this movie - it has some good parts (The clinical test of the blood substitute, for example. And the smartness of the humans carrying crossbows because, yeah that is the perfect weapon in a world full of vampires.) Just go in with your expectations in the right place.