Underworld (Frightmares, No. 8)

When siblings Charlie and Mariah Cartwright stumble upon a mysterious tunnel in an abandoned mine on their family''s property, they never imagined it would lead them to an entire underground city. Beneath the Earth, they discover New Breckenridge, a cyberpunk metropolis where sinister forces rule with an iron fist.As they navigate this strange and dangerous world, Charlie and Mariah uncover the dark truth behind the city''s rulers—the Elite Society. But when they join forces with a brave band of rebels, the siblings soon find themselves at the heart of a battle for the city''s very soul.