Worshipper – “Conquest” [Campaign 2, Mission 3]

THIS MISSION IS DRIVING ME CRAZY!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

I've already played it like a billion times!!!!!!!!!!!!!!!

I defeat everyone, the Druids are last, I have 4 Castles, and all tasks are completed (except for Agrail surviving...) but nothing happens!!!!!!!!!

What should I do?

P.S.
And what is the point of the blue key holder?????????????????