What's in the Suitcase, Grandma?: My Solar-Powered History, Book 3

You can imagine how thrilled Benson, O'Malley, and I all are when Grandma Lucy leaves her goat farm in Washington and heads up north for an Alaskan vacation. But what are the mysterious books she is carrying inside her locked suitcase?
Benson decides to find out for himself, but by the time the rest of us go after him in Dad's solar-powered history machine, Benson is lost somewhere in war-torn China.
"Will O'Malley, Grandma Lucy, and I be able to find Benson? Will Great-Grandpa Curtis stay safe when he returns to bomb-ridden Shanghai? Where is Lucy's brother, and how will he get back to his family from Japan now that a war has started?"