The Hitchhiker by Joan H. Young
In The Hitchhiker (Dubois Files book #2), Cora's family gave a hitchhiker a ride. He didn't seem to speak English, and Cora's mother thought he was ill. Then Jimmie went exploring and found more than he expected. The hitchhiker was not only sick, but he wanted the children to help him. It took four of them to solve his problem.