the last mission of Heroes of Might and Magic V and its continuation.

I finished the entire fifth installment of Heroes, and the final mission (when they defeated the Overlord) ended with them freeing Isabel, a mage creating a portal, and that's it. I read somewhere that there's a cutscene afterward showing Isabel in the same cathedral, and her eyes turn red. I have the Gold Edition of Heroes 5 (Heroes 5, Heroes 5: Hammers of Fate, Heroes 5: Tribes of the East), and I also installed a separate shortcut, "Heroes 5 Dark Messiah Mission." Is this the continuation of Heroes 5? When I launch it, I immediately see a cutscene (a conversation between two Necromancers, one of whom looks like Marcus). Is this the continuation? [6 minutes later] But when I start Hammers of Fate, Frieda and Godric are talking.