When some of their food goes bad, Julia, Lizzie, Adrian, David, and Thomas make an Anti-Aging Machine to refreshen it. Phineas begins to realize the times when he used to have fun are way past him, and begins to miss his childhood. Phineas accidentally walks inside the machine and becomes a kid again. Phineas agrees to change back after him and the kids play, but Mr. Biz attempts to steal the machine so Phineas can't change back, and he can step in as CEO of Flynn and Co. The kids have to stop him before the company replaces Phineas.