When Neverfell, who has no memory, arrives in Caverna, her facial expressions make her very dangerous to the people who live with blank faces or pay dearly to learn to simulate emotions.

Eleven-year-old Gregor returns to the world beneath New York City to rescue his kidnapped sister, Boots, and fulfill a prophecy that will restore peace to the people, bats, rats, cockroaches, and spiders who populate the underworld.

Teenager Eliza and her friends are going to explore a cave near their upstate New York home, but first her friends insist on dragging her to Drowner's Swamp, a bog legendary for its dangerous sinkholes, and a place which her mother has frequently warned her about; Eliza does not want to go, and when the earth opens up and swallows her she finds herself in a system of caves--and what she finds living there is strange and dangerous beyond anything the...

As Will Burrows continues to search for his lost archaeologist father in the strange underground world he has discovered, he stumbles across a sinister plot with terrible implications for the world above.