Amanda Valentino changed everything.

Callie Leary has exactly one thing, and one thing only, in common with Nia Rivera and Hal Bennett: They were each chosen by Amanda to be her guide. When Amanda arrived at Endeavor High, she told Callie she moves around a lot and always picks one person to help her navigate the choppy waters of a new school. Why did Amanda lie?

Following a course that they suspect Amanda deliberately plotted, Callie, Nia, and Hal piece together some cryptic clues. But they find more questions than answers and quickly realize that before they can figure out what happened to Amanda—the girl who changed their lives—they'll need to solve the most important mystery of all: Who is Amanda Valentino?