Lorey, Dean. Nightmare Academy #bk. 2

It's the monster hunters' last chance to stop an all-out monster war! We're under attack! The last of the mega-monsters known as the Named are fighting their way into our world, and only a mysterious being known as the Guardian can help-but the Guardian is dying. To save him, Charlie Benjamin and his friends from the Nightmare Academy must journey into the heart of a Hydra cave, through the spooky Bermuda Triangle graveyard, and across the treacherous, monster-filled San Diego Zoo

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