Set at the location of Deep Space Nine in the Alpha Quadrant in the Bajor Sector. You will be briefed that DS9 is currently under attack from the Mirror Universe! The team is to destroy the Mirror Invasion Fleet around DS9 and the optional is to keep the station operational.
Once the first stage is complete you will be hailed again. Stage 2 is to locate and close any portals in the area. You may have to fly around a bit to find them. Take down the Mirror ships and close the portals. Ideally, one player fights while the other closes the rifts.
You will need to close 5 portals. It is better if the whole team completes this task.
After this has been done you will be hailed again and then a major rift opens, revealing Terok Nor. Mirror Leeta will say a few words and then you will move onto the next objective.
What needs to be done here is for team members to beam up Assault Teams from DS9 and fly over to Terok Nor. Once you at Terok Nor team members will beam down the Assault Teams. You will also fire on Terok Nor and try to keep its health down. Mirror Leeta will bark orders out and taunt you in the process. One method is to have one or two on the Assault Teams and have the other 3 participants firing on Terok Nor. This is a repeating process until the next stage.
The team will need to transport down 15 Assault Teams.
Once that is done the team will approach the final stage. Mirror Leeta will state 'Our Re-inforcements will put you in your place!'. Simply take down the last batch of ships that have just come through the rift.
Advanced and Elite modes follow the same process. However, you will need to close 5 portals in order to continue. The mission will be much tougher than Normal mode.