OK, so how did the book Martha wrote survive both the fire and 118 years of existence? (No acid-free paper back then.) Both are answered simply that it was locked in a safe. Martha locked it away, intending to open the safe and retrieve the book from the airtight safe when Mavis reached her 118th birthday. After the fire, Dracula went back to see if there was anything salvageable and found the safe with the book inside. Either vampires have a magic that allows them to unlock things or he just knew the combination.
When first watching the movie, one might assume that Dracula is a standard overprotective father and the fear-mongering of humans is just a mix of boogieman-type tales and stories of angry mobs, maybe even a bit of personal experience with them. Humans are certainly built up as a sort of generic enemy that all monsters just fear out of misplaced information and past history of intolerance. Then, in a very gut-wrenching scene, we find out the truth. Dracula has a reason for what he does, and it's a damn good one. His wife was mercilessly killed by a mob, and he feels the sting of that loss to this day. It is no wonder Dracula proclaims an image of the monster-killing humans. He himself saw the heart of darkness and just what damage humans are capable of!
"You only zing once!" Is the reason why Dracula finally goes after Johnny. Fridge Horror kicks in when you realise that since he already zinged, and presumably lives forever, he's doomed to a literal eternity of loneliness. Explains a lot about both his hatred of humans and his rabid protectiveness of Mavis.