In this scene from Back to the Future Part II Marty is about to be run over, but Doc saves him.

How did Doc Brown know to drop the rope? (I read a fan hypothesis here.)

  • 1
    Looks like just a plot device to facilitate the situation - but one can always argue/speculate that because he was following he could see the situation and plan the rescue. Commented Dec 18, 2015 at 13:24
  • 1
    Fan theories are always fun, but they're no match for an actual answer based on evidence.
    – user7812
    Commented Dec 18, 2015 at 16:21
  • Suspension of Disbelief. Note, also, that much of the beginning of that clip has Marty perpendicular to the car with nothing for the hoverboard to hover off of. It defies physics, and defies what the hoverboard is even supposed to do. Commented Nov 8, 2016 at 23:33

1 Answer 1


The simple answer is that the Doc saw Marty and Biff go into the tunnel, with Marty hanging onto the side of Biff's car. He then flew over the top of the mountain to sit at the other end.

When he didn't see them come out, he rightly surmised that Marty must have let go of Biff's car and would be being chased by Biff back the way he came.

From the film's official novelisation;

So where was Marty?

Doc had kept the DeLorean hovering over the exit to the tunnel for the last minute, expecting Biff’s car to show up at any second. But there was no sign of Biff, and no sign of Marty - no sign of anything, really, except a big old truck carrying fertilizer that had gone into the tunnel beneath him.

Gone into the tunnel?

Oh no, Doc Brown thought, Marty didn’t have to come out this way at all.

He raised the DeLorean quickly. He only hoped he wasn’t too late to rectify his error.


You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .