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's The Invisible Man, 3D 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.

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's The Invisible Man, 3D 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.