It follows the adventure of Gregor and his little sister Boots, two kids who live in New York City. From the start of the story you learn that Gregor’s father is missing, and it seems that he just up and left. But Gregor soon discovers that that is not the case when his sister crawls through a rather large air vent in their laundry room. This air vent leads them to a place far underneath the City that seems almost like Hollow Earth from the Sanctuary tv series. It is a vast underground place made completely of stone.
It here that Gregor finds a city full of people, but they don’t quite look the same as us. They are called the Underlanders, as opposed to Overlanders which is what Gregor is. They introduce Gregor to a prophecy that holds the key to what happened to his father. But I won’t go into that because you’ll have to find that out for yourselves.
I personally liked this a lot. It made me laugh, and cry and a whole bunch of other things.