The stonekeeper (amulet #1) - kazu kibuishi

Emily and Navin move with their mother to the home of her deceased great-grandfather, but the strange house proves to be dangerous.

Lured into an underground world inhabited by demons, robots, and talking animals, they face the most terrifying monster of all.

The first book in Kazu Kibuishis #1 New York Times bestselling series that features a beautiful but dangerous world of new friends, giant robots, and shadowy enemies! After the tragic death of their father, Emily and Navin move with their mother to the home of her deceased great-grandfather.

The strange house proves to be dangerous.

Before long, a tentacled creature lures the kids mom through a door in the basement.

Em and Navin, desperate not to lose her, follow her into a fantastical world inhabited by robots, mysterious plants, and talking animals.

Its up to Em and Navin to figure out how to set things right and save their mothers life!.