Gregory and the gray prophecy

Beneath the streets of New York, your greatest adventure begins. When eleven-year-old Gregor tries to save his little sister from falling into a ventilation shaft, they plunge into what seems like an endless void. They land in the Underland, a world beneath New York City. There, almost translucent people coexist with giant talking cockroaches and bats. Gregor is fascinated but only wants one thing: to get back home as quickly as possible. It's already enough that his father disappeared without a trace over two years ago! Then Gregor learns that he is part of a prophecy. If he embraces it, he could not only help the Underlanders but also find his father.