So I finished the ride to the tower and saved as soon as I stood before it, with the wagon just a short distance away. The first time I did this I clicked the hand on the wagon and Graham went in. I didn't know what to do after finding the key and died.
Ok, no biggie -- that's not my problem.
The problem is that I restored my game and now... I can't get back into the wagon. I start off right where my saved game was, but now I click on the wagon and the narrator keeps saying "'Tis beyond his reach!" or somesuch. I click around everywhere, but it's a no-go. Makes no sense. Any ideas why I'm no longer able to go in?
Seems to be a glitch.
Try walking to the door, then trying to open it, or otherwise moving the camera a bit before trying to open the door.
Try running the game in windowed mode. The clickable areas may be mis-calibrated or something.
You shouldn't be manually saving or restoring during that scene at all as indicated by the window that pops up when you first begin the sequence. Just let the game handle autosaving and restoring for you until you leave the area.