Nate the Great has just received a strange musical note. The note tells Nate's friend Pip what his mother wants him to do at four o'clock. Their friend Rosamond has turned the note into a riddle. Nate checks Rosamond's garage, but doesn't find any clues. Time is running out for Nate and his dog, Sludge. It's almost four o'clock. Will Nate the Great stay stuck in the middle of this musical riddle?