Hunter and Mercy Goode are twin witches, direct descendants of the founder of their town of Goodeville. As their ancestors have done before them, it is now time for the twins to learn what it means to be Gatekeepers-the protectors of the Gates to different underworlds, ancient portals between their world and realms where mythology rules and nightmares come to life.

When their mother becomes the first victim in a string of murders, the devastated sisters vow to avenge her death. But it will take more than magic to rein in the ancient mythological monsters who've infected their peaceful town.

Now Hunter and Mercy must come together and accept their destiny or risk being separated for good.