The BBC is airing a 10-part series called The Terror that follows John Franklin as he leads an expedition to find the Northwest Passage in the 19th century. While much of it is fiction, an equal amount is fact. Some of the most unbelievable parts of the show (based on the book by Dan Simmons) are true.

Though much of The Terror is rooted in historical fact, it also contains supernatural elements, as the two vessels running afoul of an angry spirit. Here's a quick run-through of the true story that inspired The Terror's horrifying first season...