The Mary Jane Mission

When the B29 Superfortress Mary Jane is discovered in 1945 sitting in thick jungle with no visible damage, and her crew and mysterious payload are missing, the incident is hushed up and forgotten. But in 1990, mysterious radar images start to appear. F18 crews sent up to investigate discover a B29 flying towards Japan. What is this mysterious plane? If it is the Mary Jane continuing her mission, how can they stop it?