Black Mesa is a place where Gordon Freeman used to work.He was a neuclear physicist working on a portal to go to other worlds with his friends.One day,he was sent to repair the portal maker,when it imploded and monsters came out. Monster list: -Zapper(vortigaunt) -Face-Hugger(headcrab) -Gross tounge thingys(barnacles) -Longfinger(Gonome) etc, Gordon Freeman got knocked out and the monsters took over and destroyed Black Mesa.In the beginning,Gordon was being bossed around by his friends,but when the monsters came out,all his freinds died and now he goes around and kills the monsters.