The Unwritten: v. 4: Leviathan by M. J. Carey
After the shocking return of Tommy's father, the mysterious Cabal audition a new assassin and Tom seeks out the source. The source of what? He's not really sure, but it looks like a whale, and apparently it can be found in the Nantucket farmhouse where Moby-Dick was written. What he finds is a path into a whole different ocean, with more trouble (and more whales) than he could possibly imagine.