Operation: Mansion takes place in a UAF/Warcorp training facility Killhouse. As the description states, the player and his/her team were ordered to rendezvous there to begin a training operation. At the very beginning of the mission, Colonel Coleman states "You're early. The others must be dawdling." right before the player starts fighting off the Infected.
At the beginning of Round Three, a door opens behind the player's starting point, allowing another means of entry for the Infected, meaning the player must constantly check between the two doors.
At Round Six, chemical barrels detonate, destroying a barricade and allowing access to the second floor. Unfortunately, this also allows the Infected to enter the killhouse using two more doors, and quickly surround the player.
At Round Eleven, another set of barrels detonate, granting the player access to the third floor, and another door for the Infected to enter the building through.
At Round Sixteen, the last set of gates open(front gates and upstairs back gate) which as allways know allows more zombies to enter.
Despite what one would assume, this map has nothing to do with Rural Estate.
This map is most similar to Training Grounds.
If the events that take place in this map are to be considered canon, the origins of the Infected are now clouded, as Operation: Mansion seems to take place before Operation: Overdose, judging by Colonel Coleman's initial reactions to the creatures.