The Reappearance of Rachel Price meets Yellowjackets in this pulse-pounding thriller about a girl's search for her missing mother and the complicated truths she uncovers.

Sienna Benson doesn't exist.

At least, that's what her dream school says when they can't verify her identity. But Sienna knows exactly who she is—and once upon a time, a quarter-million followers did, too. Her entire childhood was posted on My Little Mini, her mom's old Instagram account, for anyone to see. How is that not proof enough that she's real?

But then a mysterious letter sends her mom running off into the night. Her mom doesn't return, but the letters keep coming. Letters written by someone named Mallory. Letters that tell a story Sienna's heard before, about nine schoolgirls who went missing in the wilderness, but only four made it out alive. Letters, Sienna realizes, about her mother.

As Sienna searches for her missing mom, she must confront the truth of who her mother is and what she's done—not just all those years ago, but with My Little Mini. And if her mother truly is the monster everyone says she is, what does that make Sienna?