Edgar Tooms's summer vacation is cut short by a supernatural home invader-a ten-foot-tall praying mantis!The voracious beast, an ancient Mesopotamian demon, is after Edgar's grandfather, a housebound ghost with no body. After escaping the creature's claws, Edgar realizes that the gigantic mantis will never stop. Luckily, the demon's entry into our world sparks a mystic transformation within Edgar, giving him a fighting chance.

Boosting Edgar's odds are the addition of his best friend Clara Diaz, and her quirky Aunt Ginnie, and the enigmatic professor Sol Balam who all bring their own special gifts to the fight.But hope fades when an even more powerful demon joins the hunt for Edgar's grandfather. Now, Edgar must travel to the Underworld to seek help from a banished race of creatures hungry for revenge against their Mantid overlords.

Time isn't on Edgar's side as the cunning demons close in for a final showdown that threatens his friends and family. Will their combined efforts be enough to save Edgar's beloved grandfather or will everyone lose their heads?