 The children begin their first day of fourth grade and are dismayed when their new teacher, Ms. Choksondik, is far stricter than Mr. Garrison was in the third grade. Hoping to return to those happier times, the kids enlist the help of some amateur scientists to construct a time machine that will send them back one year. Meanwhile, Ms. Choksondik, desperate to find a way to make the children listen to her, searches for Mr. Garrison, who is now living as a crazed hermit in the wilderness.