[Depicted in Young Indiana Jones and the Secret City, the fourth novel in the series published by Random House, second written by author Les Martin - released in 1990]
The following year after his expedition to France, the Jones boys (along with Herman) travel to Turkey (specifically the cities of Cappadocia, Konya, and Constantinople - now known as Istanbul), where Henry is continuing his research on the Holy Grail.
Inevitably they stumble into an evil cult living in an underground city, where they investigate a knife they believe to be linked to Cain and Abel.
Cain & Abel - In the bible the sons of Adam & Eve who each made sacrifices to God, though God favored Abel more than his eldest brother for reasons unspecified and unknown. Cain ultimately murders his younger brother, and is punished and cursed by God to live the remainder of his life as a wanderer.
The motive for Cain’s crime is presumed to be jealousy, and Cain is considered to be the first child of Eve, the first murderer, and the first human being to ever fall under a curse.