Jasper discovers a perfect-looking purple crayon in the gutter on his way home from school. Miraculously, the purple crayon seems to be helping him pass his math and spelling tests (for which he didn't study) and helping him improve his work. But over time, the crayon becomes increasingly intrusive and demanding of Jasper's time, and when it begins changing his artwork--the one area where Jasper excels--he knows he has a problem on his hands. However, getting rid of the crayon may prove more challenging than picking it up.