The main game currently has 13 missions, divided into 3 acts, each with a final Boss.
There are 13 missions intentionally, as 13 is the sacred number of the Horned Rat, the Skaven god.
After defeating the Boss of each act, you can progress to the final mission.
Missions can be played on four difficulties, five with the DLC Winds of Magic.
The first DLC, Shadows over Bögenhafen, has added two missions. The second DLC, Back to Ubersreik, has added three more. The third DLC, Winds of Magic, adds one new mission
There is also Taal's Horn Keep, the home base of our heroes, and the Prologue level is played automatically the first time you start up the game and available through the main menu for repetition.
Shadows over Bögenhafen
Back to Ubersreik
Winds of Magic
The Curse of Drachenfels