The protagonist, Harold, is a curious four-year-old boy who, with his magic purple crayon, has the power to create a world of his own simply by drawing it. Harold wants to go for a walk in the moonlight, but there is no moon, so he draws one. He has nowhere to walk, so he draws a path. Using his purple crayon, he goes on many adventures including encountering a dragon, boating through deep waters, eating a picnic consisting only of nine flavors of pies, and flying in a hot-air balloon that saves him from a fall. Eventually Harold grows tired, and searches for his bedroom window in order to go to bed. He draws many windows, drawing an entire city, yet none is his. Finally, Harold remembers where his window is situated and constructs his own room and bed, and nods off to sleep.