15-year-old Penelope Greene had no real name before Dr. Cruz. She was only called "Subject 5945743." As long as Penelope can remember she has not known anything but the harsh gray walls of her cell, needles, and pain. She also has the mark of a strange bird on her left calf.

After years of torture the bird on her leg appears to her. The bird--who she now knows as a magpie--whispers the way out into her ear. With Dr. Cruz's help, Penelope escapes into the forest surrounding the lab. Now she has to find her way out of a seemingly never-ending forest and evade her pursuers.

Will she be able to escape? Or will the people hunting Penelope never stop? And they know something she doesn't. They know Penelope has the power to destroy the world.