Nearly 25 years ago, Nnedi Okorafor was visiting relatives in Isiekenesi, Nigeria, when she asked her grand uncle a sensitive question. What could he tell her about Nsibidi, an old and often secret symbolic script?

“His response was, ‘You should not be asking me about these evil things!’” Ms. Okorafor recalled.

Predictably, his chiding only fueled her curiosity. She learned everything she could about the script and, many years later, incorporated it into her fantasy books. “There’s a secretness that was really intriguing,” said Ms. Okorafor, who has a tattoo on her arm with Nsibidi symbols that means “story teller.”

Magic, ritual and secrecy are threads that run through Ms. Okorafor’s wildly imaginative young adult fantasy series, which features a head-spinning menagerie of otherworldly spirits and deities drawn from Nigerian myths and legends.

This week, Viking published “Akata Warrior,” the second book in the Akata series, a dark, sprawling epic that some fans and readers have labeled the “Nigerian Harry Potter.” The story centers on Sunny Nwazue, a Nigerian-American girl who moves to southeastern Nigeria from New York, and learns that she belongs to the secret Leopard Society, a group of people with magical abilities. An albino with pale skin and hair, Sunny is treated as an outcast by superstitious locals who call her a witch. But once she discovers her powers, she becomes friends with three other Leopard children, learning to cast spells, read Nsibidi and move between the physical world and spirit realm.