Half-Life Blue Shift is an expansion pack for Valve Software's science fiction first-person shooter video game Half-Life. The game was developed by Gearbox Software and Valve Corporation. Blue Shift is the second expansion for Half-Life. Blue Shift returns to the setting and events of the original game, but portrays the story through the eyes of another person. The protagonist in Blue Shift is a security guard, Barney Calhoun, employed by the Black Mesa Research Facility. After a scientific mishap causes Black Mesa to be invaded by aliens, Calhoun must fight his way to safety.