is a fantasy-mystery drama that follows Han Tae Sool, a genius engineer who embarks on a perilous journey to bring to light hidden beings that are secretly residing in our world, and  Tae Sool's savior Kang Seo Hae, who has walked a long and dangerous path for him.At some point in their lives, everyone has asked themselves the question, "What if we could go back to the past?