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, Pip's piano teacher, has turned the note into a riddle.

Nate the Great is on the case. He checks Rosamond's garage but doesn't find any clues. Later, Nate and his trusty dog Sludge don't see or hear anything strange at the band concert.

Time is running out. It's almost four o'clock. Will Nate the Great stay stuck in the middle of this musical riddle?