Mistake of Pythagoras

Mistake of Pythagoras is a modification for Half-Life 2, developed by Koumei Satou. Something goes mad because the human race failed in the experiment, and it connects with another world. The resident in the another world is crazy due to the mistake. We should restore the situation.

You are Gordon in a parallel world and the city is under attack from unknown enemies. You have to find out a way to stop the invasion by traveling into their world and correcting the “mistake.”