While on vacation in Istanbul, Turkey, the members of Mystery, Inc. go to see Butch Cassidy and the Sundance Kids, the famous all-Jewish rock band that just arrived in Istanbul. Mystery, Inc. actually meets the band in person and is confused as to why they are in Istanbul since Turkey is an Islamic country. That night, the Ghost of Justinian arrives and goes after Mystery, Inc. Just as the ghost has them cornered, the Sundance Kids arrive and rescue them. Butch Cassidy then reveals that he and his bandmates are really agents for the US Government who are investigating the ghost. The two teams decide to join forces to stop this ghost. But can they stop the ghost?
Merilee's last name is revealed to be Mendelssohn.
Stephanie's last name is revealed to be Heifetz.
Wally's last name is revealed to be Bernstein with the "ei" pronounced with a long i sound.
It is also revealed that Stephanie and Wally have the same mother but different fathers which explains their different last names because in the original TV series, Butch Cassidy and the Sundance Kids, Stephanie and Wally were siblings. Both their fathers are still alive, and Stephanie's is divorced.
The decision to make the Sundance Kids all Jewish was bound to contradict the original series which is why it was revealed that Stephanie and Wally were converted to Judaism by their fathers. Their mother is a Presbyterian from Scotland.
At the end of the episode, Butch Cassidy says to the Mystery, Inc. gang, "If we ever have another difficult assignment, I will have the pleasure to ask for your help."