In 2015, humanity has no idea that a massive catastrophe is about to occur, resulting in a significant reduction in the Earth's population. A deadly virus claims the lives of millions, and those who remain alive are forced to hide underground. In 2043, humans still cannot determine the origin of this infection or who the "patient zero" was. However, in the future, scientists have succeeded in developing time travel technology. Now, a group of enthusiasts intends to test their invention and change history.