Since I just remembered the scene where the hero and the heroine find something in the library and then realize that the enemy is coming, and they have to bolt. One of the first things I thought of, before I started to outline, but I didn't note it down.
To be sure, they are now surrounded by enough forces that either she would not be allow back in with the hero in tow, or (if she managed that) the enemy forces would have to be faced because that many men could not bolt secretly enough -- and besides, they might win.
At which point, I remembered that I was stymied with the heroine trying to figure out what the stones are. Nothing could be more natural than sending her off with a small group to find out. They're not so overflowing with resources that they can neglect the stones.
And -- hmm -- I had the idea of one man proving a traitor, and this is a good spot, to pare down the characters.
The heroine, however, will not be using the flight stone with its wings. Yet. 0:)