Fred is a sixth-grader grieving over the loss of Casey, his beloved dog. Every day he walks home from school bouncing Casey's old worn-out ball. One day, the ball falls down a grate. When Fred tries to retrieve it he enters a parallel world: Casey is alive, his mom, sister, and there's a version of Fred too. Spending time with Casey, Fred feels happy for the first time since his dog's death, but he slowly realizes that the loss of Casey is masking an even greater loss: the death of his dad. Fred brings his sister, Izzy, to this upside-down world of lost things in the hope of finding their father and bringing him back. Can everything that is lost be found again?