A little boy takes a walk, using his purple crayon to create everything he encounters along the way. He draws a forest with only one tree, a dragon who guards the apples on the tree. He creates an ocean and a sailboat to navigate it, land to land on. On the land a picnic with nothing but pies, a hill with only one side, a hot-air balloon to save him from a fall and a big city with lots of windows. But none of the windows are his, and it's time to go home. Finally, he draws his own window and his own bedroom and his own bed and goes to sleep.