Daryl Gregory 
Harrison Squared [EPUB ebook] 

Harrison is a lonely teenager, afraid of water ever since a boating accident as a toddler. And he and his mother have just moved to the worst possible place: Dunnsmouth, a Lovecraftian town on the Atlantic coast. When his mother disappears, Harrison tries to solve the mystery, putting him in conflict with a strange church, a killer, and the Deep Ones… It will take all his resources—and an unusual host of allies—to defeat the danger and find his mother.