A ‘doppelganger’ is a German word for a ghost double.  In this book by the same name, the doppelganger is Brian Bain, a 13-year-old who was born in Korea and adopted twice in the U.S.  His first birth family died in an accident when he was very young, and he was then adopted by his guardians.  Brian doesn’t know much about his real background, other than he was born in Korea.  After winning a design contest, Brian’s picture is in the local newspaper.  This causes him to be contacted by  strange strangers who think he is someone else.  His friend, Roni, finds an old photo on-line of a little boy these strangers ask him about; she ages it to Brian’s age and there is his doppelganger — a boy who looks like him exactly.  At first, he thinks it’s a case of mistaken identity.  But to complicate matters, a family has offered a $100,000 reward for information on his whereabouts (or his doppelganger).  This pricetag is what is causing the nuts to come out.  What Brian finds out is that he actually has a twin who has disappeared.  The story has a lot of action but the main ideas don’t get lost.  A very entertaining and suspenseful read for those who enjoy mysteries.