Uninvited guests.

I seem to be having bad luck with your map. I decided to play it again, and this time, I couldn't hire dwarves in two "houses" right away. However, I managed to defend against three attacks on the castle, but I couldn't defend against the fourth (which followed immediately after the third) – the computer captured the castle in the same turn, even though my hero was inside it after the victory (meaning there were two attacks in one turn).