Jaded 74-year-old reptile Leo has been stuck in the same Florida classroom for decades with his terrarium-mate turtle. When he learns he only has one year left to live, he plans to escape to experience life on the outside but instead gets caught up in the problems of his anxious students — including an impossibly mean substitute teacher.

Inside of his book, adventurous Harold can make anything come to life simply by drawing it. After he grows up and draws himself off the book's pages and into the physical world, Harold finds he has a lot to learn about real life.