The secret of the soldier's gold - #182 (1st Aladdin Paperbacks ed.)

While on a trip to Portugal with their father, the boys go on their own hunt for gold bars, a treasure that was buried in Mrs. Rilke's childhood backyard after World War II by a defecting German soldier.

Someone else has found out about the treasure and is searching for it also.

Can Frank and Joe find it before. it falls into the wrong hands?.