I've suddenly realised, looking at some of the other threads, that we may be playing this bit differently to the rest of you.
We play that "discard an ally" means "put the ally back in the ally deck". Looking at people's interpretations of Joining the Winning Team (mission: discard 4 allies to pass), The Stars Are Right (rumour: discard an ally to pass) and even Duke (ally:discard to restore sanity), it seems the more common interpretation is it means "put the ally back in the box". I've looked through the rules and FAQs a few times: am I missing something, or is this just a very common house rule to make things slightly harder (and perhaps more thematic, too).