The sequel to Monster Hunter International. So -- spoilers for that ahead.
So Owen and his team are doing all right in Mexico, when a shadowy man tries to abduct him from the hotel, because his Overlord ordered her, and an outbreak of zombies gets Owen under arrest because they need to blame someone. And in jail, his fiancee's parents break in, which is kinda of trouble, since (here's a spoiler for the last) they're a pair of vampires. Fortunately for him, the federal forces come to bust him out because -- it turns out -- they need bait.
Seems that last book, Myers had launched an atom bomb into the gap in reality. This annoyed the Old One, and it blamed Owen, and sent a message to a mortal cult that worships him, and has nasty magic. (See shadowy man mentioned previously.) So Owen's stuck at the compound with four agents -- one of him is the ever favorite Agent Franks.
The cult goes after his family.
The story winds out on from there. It includes Julie's childhood not-so-imaginary friend, Agent Frank's origin, the origin of gnomes (household spirits? try protection racket), old secrets from before Owen joined the MHI, a rushed wedding followed by orders to Owen to carry out an orcish wedding custom, the discovery of what was destroying the mind of an erstwhile Hunter, a truly ghastly tree, and much more.