Top Ten Military Encounters: A fascinating and shocking countdown of the top ten military encounters between Earth's armed forces and UFOs. (S2, ep 6)

The Shoot Down Order: Jets are scrambled to intercept a UFO, but find they are unable to complete their Shoot Down Order. (S4, ep 5)

Alien Apocalypse: If extraterrestrials visited Earth would they enlighten us or destroy us? Experts examine the possibility of a doomsday orchestrated by an alien enemy. (S2, ep 5)

Atmospheric Anomalies: Some experts believe many atmospheric light shows are actually caused by extraterrestrials. If so, do they pose an imminent threat to humanity? (S2, ep 4)

The Freedom of Information Act: In 1969, the US government officially announced it would stop investigating UFOs, but declassified documents seem to tell another story. (S4, ep 3)

Astronaut Encounters: To this day, NASA denies all UFO accounts and has taken measures to prevent its astronauts from telling their stories. But what are they hiding? (S2, ep 3)

The 1952 Wave: In Spring 1952, reports of UFO sightings shot through the roof. Can former US Air Officials shed any light on this? (S4, ep 2)

Human Harvest: A look at frightening reports of alleged alien abduction, including cases in which abductees claim to have been subjected to torturous medical experiments. (S2, ep 2)

Second Skin: To enter space, humans require a space suit. Are the aliens that are said to have visited earth any different? Or are they more akin to artificial drones? (S4, ep 1)

Alien Origins: The compelling series returns to examine more eerie reports of UFOs. Can it determine where in the universe such strange flying crafts could be coming from? (S2, ep 1)