Black Mesa: Blue Shift

Half-Life: Blue Shift follows Barney Calhoun, a Black Mesa security guard, beginning on the same day as Freeman's experiment. The resonance cascade traps Calhoun in a failing elevator that drops him deep into the facility. He fights his way up toward the surface and connects with Dr. Rosenberg, a scientist who has a plan for escaping Black Mesa using a prototype teleportation system. Freeing Rosenberg from Marine custody, reaching a decommissioned lab where other survivors have gathered, and calibrating the teleporter by traveling to the Xen border world are the steps between Calhoun and survival. The teleporter's destruction during a Marine assault sends Calhoun into a harmonic reflux — a rapid cascade of involuntary teleportation through locations in both Xen and Black Mesa, including a moment where he witnesses Freeman mid-way through the events of the original game — before finally stabilizing outside the facility.