The plot deals with the events leading up to Tess's fifteenth birthday, the day on which all Switchers lose their powers forever, and must choose a permanent form in which to spend the rest of their lives.
At her cousins' farm, Tess discovers that the house is infested with rats, which enrages her (easily angered) uncle Maurice, who is planning to sell the nearby wood for development.
Tess explains the situation, and he informs her of his belief that an ancient, magical presence may be abroad in the woods, one which even they, with their experience of the supernatural world, have never imagined.
One white rat (identifying herself as "Cat Friend") transmits an image of four pairs of feet, which Tess recognises as Colm's, Orla's, Brian's and, unfortunately, Kevin's.
Tess tracks down Cat Friend, but is surprised when the rat provides her with an image of her cousins and Kevin walking straight through the face of a crag.
With Declan, Tess discovers the true extent of her powers and her heritage: She learns how to Switch other objects, how to control the weather, and how to ride the wind, as well as dancing with her immortal ancestors on Ben Bulben.
With the moment of her fifteenth birthday only a few minutes away, Tess rides the wind back to where Kevin waits, informing him of her choice to remain a fairy.
Kirkus Reviews wrote: "The story develops slowly compared to the first two installments, and stands alone only by virtue of repeated back filling, but readers will see how tempting each of Tess’s options are, and how her previous experiences influence her eventual choice.
"[2] Sally Estes of Booklist wrote that while the "scenes of Tess in her various animal personae, as well as the overall feeling of dread that permeates the story, are well handled", the conclusion is "heavy-handed and overly tidy.
"[3] Tina Hudak of the School Library Journal wrote that the novel "will appeal to pre-adolescents especially, as Tess must decide between her own narcissistic desires or being a voice for the earth's wild creatures" and that it "illuminates the complex psychological dilemmas of changing family relationships.