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Your Gordon freemen a former scientist at the black mesa, after the invasion you escape and take a new job from the mysterious G-man and are quickly teleported to another BM funded facility the "Black mesa xen life forms test facility (C1) a highly defended lab built into one of the asteroids of xen!with a ring of 18" cannons surrounding the complex ?the defense ring?. You are headed to the test lab on your first day and everything?s going great but then BOOM!! CRASH!!!! AHHHHHHHH!! The whole complex is invaded by the aliens outside you'll have to fight your way out of the underwater sector of the base and to the surface good luck you'll need it.