After her hand is amputated following a tragic accident, Rachel Cooper suffers vivid nightmares of a woman imprisoned in the trunk of a hollow tree, screaming for help. When she begins to experience phantom sensations of leaves and earth with her missing limb, Rachel is terrified she is going mad... but then another hand takes hers, and the trapped woman is pulled into our world.

This woman has no idea who she is, but Rachel can't help but think of the mystery of Oak Mary, a female corpse found in a hollow tree, and who was never identified. Three urban legends have grown up around the case; was Mary a Nazi spy, a prostitute or a gypsy witch? Rachel is desperate to learn the truth, but darker forces are at work. For a rule has been broken, and Mary is in a world where she doesn't belong...