The Littles Go Exploring / Peterson, John

"Grandpa Little disappeared many years ago. Everyone says he is probably dead... except Granny Little. But when Tom and Lucy, the littlest Littles of all, find a secret room filled with papers belonging to Grandpa Little, they think that maybe he's alive after all. If the Littles read his diary and study his maps, can they find Grandpa Little or will he be lost forever?"--Back cover.

Despite the fact that Grandpa Little has been missing for a couple of years, the Littles begin to wonder if he might still be alive after finding a secret room where he apparently used to visit.