S1, E3: The 1893 Chicago World's Fair was a triumph of architecture and technology that offered 27 million amazed visitors a preview of 20th century. But a mere mile down the road from the fair, one man, H.H. Holmes, was making history in a far more sinister way. He had built a hotel designed for murder, which would later be known as "The Murder Castle." It was a three-story, block-long hotel designed with trap doors, gas chambers and vats of acid all meant to aid a madman in his efforts to murder 200 people. Today, the spirits of Holmes' forgotten victims appear to astonished witnesses, attempting to tell the truth behind a story that remains shrouded in mystery over 100 years later. From Holmes' hometown in New Hampshire, to the site of his hotel in Chicago, to the final resting place of his youngest victim in Indiana, voices and visions reveal the shocking truth behind one of most evil men in America's history and the country's first serial killer.