If you draw a Treachery card during:
- Setup of Scenario 2, where you add some cards to the staging area
- Setup of Scenario 3, when you are adding an encounter to each objective
So far we've been playing as if the Treachery was ignored and another card is drawn in its place (so Scenario 2 *always* has the right number of cards in the staging area at the start, and each objective *always* has an encounter on it) but I'm not really sure. Does it say somewhere in the rules that I've missed?