Sixteen-year-old Joey Harker has just saved the Altiverse—the dimension that contains all the myriad Earths—from complete destruction. After mastering the ability to walk between dimensions, Joey and his fellow InterWorld Freedom Fighters are on a mission to maintain peace between the rival powers of magic and science who seek to control all worlds.

When a stranger named Acacia somehow follows Joey back to InterWorld’s Base, things get complicated. No one knows who she is or where she’s from—or how she knows so much about InterWorld. Dangerous times lie ahead, and Joey has no one to rely on but himself and his wits—and, just maybe, the mysterious Acacia Jones.

Full of riveting interdimensional battles, epic journeys between worlds, and twists and turns along the way, this sequel to the New York Times bestselling InterWorld is a thrilling, mind-bending adventure through time and space.