In 1845, maverick sea captain Sir John Franklin set off with 128 men on Royal Navy ships HMS Erebus and HMS Terror, to chart the elusive Northwest Passage. Venturing into uncharted Arctic waters, they were sailing off the map of the known world. Their state-of-the-art mission was equipped to survive for up to three years, but they were never heard from again. A century and a half of searching revealed only scant and tantalising clues, suggesting a descent into madness, starvation and even cannibalism. But no trace of the ships was found, until, 170 years later, a multi-million-dollar state-of-the-art expedition astonishingly found HMS Erebus, intact and upright on the Arctic sea floor. This Secret History documentary has exclusive access behind the scenes of that momentous expedition, revealing the dramatic chain of events that led to their historic discovery.