Inga Arvad was the great love of President John F. Kennedy's life, and also Adolf Hitler's special guest at the 1936 Berlin Olympics. She was an actress, a foreign correspondent, a popular Washington columnist, an explorer who lived among a tribe of headhunters, one of Hollywood's most influential gossip columnists, and a suspected Nazi spy. The latter nearly got Kennedy cashiered out of the Navy, but instead set in motion the chain of events that...