A young woman studying the habits of webcam chat users from the apparent safety of her apartment witnesses a brutal murder online and is quickly immersed in a nightmare in which she and her loved ones are targeted for the same grisly fate as the first victim.

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, National Geographic 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.