This is the third book in the "Dracula Returns" series. To the best of my knowledge, there are nine in total, and I would strongly recommend reading the previous two books first.
In this story, a pair of villainous brothers have created a flock of mutant vampire bats and are sending them to kill people until the government pays them a ransom. Naturally, Professor Harmon tries to persuade Dracula to dispose of both the bats and the brothers. However, Dracula is reluctant to harm the bats because he feels a kind of kinship with them.
Like the other novels in the series, this one is light on character development, with the focus being on the action and plot. fact, even though it is classified as a horror, it reads more like one of the old pulp stories from the 1930s and 1940s. I don't think there is anything wrong with that, and I stories like this a fun bit of escapism. Dracula himself is thoroughly evil, just the way I like him, and only helps the good guys because of a deadly device surgically implanted next to his heart.
Overall, it is a short, fast-paced action/horror novel, and I am looking forward to reading the rest of the books in the series.