The Stonekeeper by Kazu Kibuishi

After moving into their great-grandfather’s creaky house, Emily and her brother Navin are thrust into a hidden world when a sinister creature drags their mother below. Guided by a powerful amulet that grants Emily dangerous new abilities and whispers of control, they team up with quirky robot companions to navigate the underground city of Alledia, battle ruthless enemies, and race to rescue their mother—while Emily struggles to decide whether she will master the stone’s power or be mastered by it.

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