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?
The sun is shining, the birds are singing, and someone is eating the flowers in Nate the Great's garden. A green tortoise is slowly, slowly stepping across the lawn, and Nate is slowly, slowly following him. Where does Nate's green guest truly belong? It may take all of Nate the Great's patience and sharp eyesight to find out slowly.