I have the original CD release of HoMM3 Complete.

I just finished the subcampaign, "Unholy Alliance." It's my understanding there's supposed to be a final sub-campaign called "Specter of Power." However, after completing "Unholy Alliance" I was simply dumped back to the main menu.

I admit that I modified the difficulty of some of the individual missions as I played through the campaigns. Does the game penalize you for doing that by withholding "Specter of Power?"

I figured it out.

So, part of the complication may be this: I was using the HoMM3 HD mod. That may have affected things.

When you finish Unholy Alliance, the game may dump you to the main menu. However, if you load the saved game it prompts you to make at the end of Unholy Alliance, then Specter of Power will be available to choose and play.

It's not related to the HD mod, I had the same problem in the vanilla version. When Unholy Alliance is finished, the game throws you back in the main menu rather than the campaign menu like it did for every other campaigns in the game, the only way you can unlock it is to load the savegame you made when you finished the twelfth mission of Unholy Alliance. I wonder how many people missed that campaign because of that.

Okay thanks, I've just had the same problem and had a mild heart attack because I was trying to find SoP and didn't see it. All the other Google searches pretend like you go right into it.