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From old-school "dead drops" to high-tech digital transfers, this is a look at how intelligence officers actually acquire the information collected by sources.

Paranoia spirals out of control as the demonic force terrorising Salem grows. Suspected witches are jailed and the accused face execution if found guilty. (2 of.

A secret military base is discovered a few hundred miles from the North Pole, while a man-made stone formation is found 120-feet below Lake Huron.

For centuries, cultures around the world have believed in stargates through which beings have travelled to Earth - but could such portals truly exist.

Experts question whether the notion of rituals, such as funerals and festivals, was brought to earth by ancient extraterrestrial visitors.

Set sail for Rathlin Island as we explore a Neolithic stone tool factory, a unique upside-down lighthouse and a World War II shipwreck. (3 of.

Dan delves into the rich past of the Tower of London, exploring inside the imposing walls that have witnessed some of the most important events in our history.

Scientists in England conduct groundbreaking séances, while someone returns from the grave.

A father and son see mysterious lights near their property and call the sheriff's office. A large craft covers a French town in an odd material.

Local authorities receive over 50 UFO reports in the Chicago area on Halloween night. Multiple sightings of a large flying craft in PA are known as the Buck's County Wave.

For decades, claims of extraterrestrial presence on Earth have been made - and the government have gone to great lengths to discredit them.

Experts investigate an ancient fortress in Peru said to have been built with laser tools. Could it prove that aliens once visited Earth.

Churchill must make crucial decisions and figure out how to navigate big changes as the war rages on and Britain makes a powerful ally. (3 of.

George Blake: While in a North Korean prison, George Blake was recruited by the Soviets to spy on the British. He was caught but escaped to the Soviet Union.

From ghostly voices to vanishing UFOs, experts investigate puzzling and mysterious signal interferences and break down the meanings behind them.

For decades, claims of extraterrestrial presence on Earth have been made - and the government have gone to great lengths to discredit them.

Experts investigate an ancient fortress in Peru said to have been built with laser tools. Could it prove that aliens once visited Earth.

Starting on the Isle of Lewis in the Outer Hebrides, witness the 5,000-year-old standing stones of Callanish, traditional Scottish blackhouses, and cut peat with a modern crofter. (2 of.

...Hate The English? Ireland: Al meets up with Andrew Maxwell to explore the fierce animosity between the English and their Irish cousins.

Churchill must make crucial decisions and figure out how to navigate big changes as the war rages on and Britain makes a powerful ally. (3 of.

From the trench to the home front hospital, a medical historian retraces the train journey made by wounded soldiers during World War I.

A sword discovered at the bottom of a river may be the famed Excalibur. Also, a doorbell cam captures possible proof of teleportation.

Malaysian Toilet Monster & The Buzzer: A large black creature emerging from a family's toilet could be some kind of mythical creature. An astronaut spots something intriguing.

Embark on an eye-opening journey as experts investigate the startling mysteries captured by satellites orbiting the Earth: from hidden worlds to unexplainable natural phenomena.

A couple spot a huge blimp-shaped craft hovering over Michigan's Lake Erie in 1988. In 1963, two sisters and their housekeeper report being knocked down by a UFO emitting flames.

In 1993, a teenage girl walking her dog in Shropshire, England, witnesses a cylindrical object in the sky. School kids in Florida report multiple UFO sightings in 1967.

Explore moments, motives and ramifications in war that have shaped recent history, from World War I and "the eleventh day of the eleventh month" to Operation Desert Storm.

Imagine free falling 30,000 feet, or being buried alive and living to tell the tale. These are some of history's most incredible survival stories.

Experts study previous reports of zombies, vampires and spirits. Could these sightings of the undead actually have been alien encounters.

The Quest for the Holy Grail: As the Third Reich rises to power, Himmler fixates on the Holy Grail as his and the Nazis' desperation to capture this ancient relic intensifies.