The Adventures travel back to Chicago in the prohibition era, where both Gangster Al Capone and Eliot Ness, Chief of the famous "Untouchables", are attracted to an opera singer. An opera performance and then a wild ride through the streets of Chicago give the Adventurers a firsthand taste of the late "roaring twenties". The kids also manage to prevent an attempt on Ness' life by the legendary Al Capone.