What if an extra-terrestrial force attacked Earth? What might that look like and how will the people of Earth respond? Consulting a cast of world-renowned scientists, survival experts and defense experts, this two-hour special, Alien Invasion explores this frightening scenario. Experts reveal what could motivate alien invaders to attack Earth, and speculate on how the attack might play out -- the strategy alien invaders might use and the most effective ways for humans to respond. We'll turn to science and history to figure out what works. We'll show how humanity can survive this ultimate test.