Spring semester at the Lab School in Hyde Park finds Petra and Calder drawn into another mystery when unexplainable accidents and ghostly happenings throw a spotlight on Frank Lloyd Wright's Robie House, and it's up to the two junior sleuths to piece together the clues. Stir in the return of Calder's friend Tommy (which creates a tense triangle), H.G. Wells' Invisible Man, 3-D pentominoes, and the hunt for a coded message left behind by Wright, and the kids become tangled in a dangerous web in which life and art intermingle with death, deception and surprise.