6. How Did Old Biff Return The Delorean to 2015?
In Back To The Future Part Two Marty buys the sports almanac with the intention of placing a few bets in the past and guaranteeing hell win. The Doc goes all moral on him and slaps him on the wrist, but unknown to them Old Biff is overhearing this and hatches his devious plan to make himself rich in his youth. Old Biff takes the almanac from the trash, steals the Delorean and successfully goes back in time to 1955 where he gives young Biff the book of sports facts. Having done this Old Biff then returns the time machine to 2015 where Marty and Doc use it to go to back to 1985. Once there they discover that the 1985 they have arrived in is the future based on how old Biff had changed the past in 1955. How was old Biff able to return the car to 2015? The Doc warns Marty in the bad 1985 that they cannot stop old Biff in 2015 as it would be the future of the bad universe, so how was old Biff able to return the car to the good version of time and not just wind up in a version of 2015 where he was already rich and powerful?