This is the second book in the YA Peter Normal Series by [a:Darren Pillsbury|965480|Darren Pillsbury|http://d.gr-assets.com/authors/1331738190p2/965480.jpg].
Peter and his friend Dill find themselves in the middle of a vampire mystery that has been part of their town lore for centuries. Eventually, they have to pull Peter's grandfather into the mix to help them get out of the mess that they find themselves in. There is a lot more to grandfather than they expected.
A very dark YA series. And very fun.
I read this as part of the collection of Peter Normal stories in
[b:Peter And The Vampires|12150434|Peter And The Vampires (Volume One)|Darren Pillsbury|http://d.gr-assets.com/books/1328562530s/12150434.jpg|16289776].