Thanks Tally Ho and Syd, I'm going to try this a few more times before I give up. I think I finally figured out the correct path, I can chase him (running) until I see him dash across the bridge, then Poof! everything goes gray again. I guess I just have to move faster and not crash into any walls as I run around the building.
(Syd, I'll let you know if I need a saved game. This is beginning to remind me of Atlantis, The Lost Tales.)