Have humans really seen space-crafts and beings from other planets? Or is there a perfectly reasonable explanation for these sightings? Despite seeming like the stuff of science fiction films, the fact remains that there have been numerous real-life reports from people claiming to have seen unidentifiable air-crafts and mysterious airborne objects. Many have been dismissed as the products of unreliable witnesses or hoaxes. But a few are harder to explain away. Invasion Earth investigates the world's most intriguing UFO sightings to answer the age old question – are we alone? With the help of scientists, aviation and military experts, all the evidence is thoroughly examined and tested.