In his book, the adventurous Harold possesses the ability to bring anything to life with his drawings. As he matures and sketches himself out of the book and into the real world, Harold discovers that he has much to learn about reality. His reliable purple crayon, however, might lead to more comedic chaos than he ever anticipated. When the boundless power of imagination is misused, Harold and his friends must use all their creativity to rescue both the real world and his own.