(Casting mostly with Half-Life 2 and its episodes in mind.)
After accidentally causing an inter-dimensional alien invasion from an experiment gone wrong at the Black Mesa Research Facility, Gordon Freeman fights to clean up and stop the resulting catastrophe all while evading a military cover up. Afterwards he is approached by a mysterious man with supernatural powers and "employed" under him, getting sent 20 years into the future to fight with his former colleagues against another worse alien empire, the Combine.
