Nine-year-old Shelby Holmes and eleven-year-old John Watson team up again, this time to investigate the new science teacher at the Harlem Academy of the Arts. In the few weeks since moving to Harlem with his mom, Shelby has been training John in the art of observation-a skill that comes in handy on the first day of school. John's new teacher, Mr. Crosby, is acting suspiciously, and Shelby knows this is a mystery worth investigating. But as Shelby and John dig deeper, they discover that there may be someone unexpected involved--someone who may have Shelby beat.