Indiana Jones and the Last Crusade (junior novelization)

Publisher's summary
''This time, Indy's on a rescue mission: his father has gone missing on a quest for the Holy Grail, and Indy must put the clues together to locate him. His exploits put him on his father's trail, but treachery isn't far behind. Soon, Indy finds himself walking right into a trap, and he'll have to team up with his father to make it out alive.''