When twelve-year-old Leah goes to spend the summer in Chicago with her little cousin TJ, she's shocked to discover that he's gone mute after surviving a school shooting. She knows there isn't a "right way" to deal with his pain, but when she learns that he's sneaking out to visit a laundromat at night, it seems all wrong.

Determined to discover why the laundromat brings her cousin to life, Leah and her new friend Violet follow him, unwittingly falling into an imaginary world called "The Land of Lost Things," home to the socks and coins and buttons that disappear in the dryer. And when TJ hears about the wonders beyond the portal in the back of the dryer, he actually speaks!

Eager to keep him talking, Leah and her new friends populate the world with characters, performing elaborate puppet shows that grab the attention of YouTube viewers everywhere. Soon Leah realizes that there's something in this special world that TJ has to find and get back. But as the Lost Things Club works together to try and make TJ's dreams a reality, they learn there are some lost things that can't come back.