The setting is the playground at a day-care center. The lost-and-found box is the home of a creature called "Lou" for the missing letters on the outside of the box, which says "_OST & F__ND". Lou is a sentient being formed by all the odds and ends in the box—a red sweatshirt that forms his body, two different-sized baseballs that form his eyes, a book that sometimes forms a mouth, and other sundries. After the kids leave every day Lou scarfs up the things they've left behind and adds to himself.
One day Lou sees a boy named J.J. out in the yard bullying other kids and stealing their toys. Lou gets mad and decides to steal J.J.'s backpack which contains all the stolen toys. A merry chase ensues as J.J. tries to get the toys back from Lou, until Lou realizes why J.J. is a bully to begin with.
Lou played in theaters in front of the Pixar feature Cars 3.
- Animate Inanimate Object: Lou is made up of all the stuff in the lost and found box.
- The Atoner: A chastened J.J. gives back not only the toys he stole, but all the toys in the box—unfortunately for Lou.
- Bittersweet Ending: A reformed J.J. gives all the stuff in the lost and found box back to the other kids, leaving the box empty, which means Lou no longer exists. But J.J. gets back his long-lost teddy bear.
- The Bully: J.J., who delights in taking the other kids' toys and laughing at them. Eventually we find out why J.J. is like that: years ago when he was a toddler a bully stole his teddy bear.
- Cessation of Existence: Lou's apparent fate after the box is emptied.
- Combining Mecha: While Lou has a single consciousness he can assemble the various objects that make up his "body" in any combination. His baseball "eyes" are usually inside the hood of his sweatshirt, unless he sends them to the ends of the sleeves. Sometimes the book is his mouth, and sometimes it isn't.
- Continuity Nod: All the children in Lou previously appeared in Pixar features Finding Dory and Inside Out. J.J. can be seen in Riley's new class in Inside Out.
- Eye on a Stalk: This effect is produced when Lou's eyes, which are usually in the hood of his sweatshirt, migrate to the end of the sleeves.
- The Faceless: The bully that picked on toddler J.J. is seen only as a vague silhouette in J.J.'s flashback.
- Flashback: How we learn why J.J. is so mean.
- Freudian Excuse: J.J. is a bully because he was also bullied in the past.
- Good Feels Good: J.J. discovers this as he returns the toys to the kids.
- Reformed Bully: J.J. becomes one at the end of the episode.
- Seesaw Catapult: Happens to Lou when during the chase he ends up on one side of the seesaw, and J.J. lands on the other side.
- Signs of Disrepair: Lou's "_OST & F__ND" box, with the missing letters forming his name.