Darkest of Days is a first-person shooter. The player controls Alexander Morris, a soldier fighting in General Custer's battalion during the Battle of Little Big Horn. After Caster is killed and Morris is wounded, he is suddenly rescued by a man in futuristic armor and taken through a strange portal. Morris then wakes up in the headquarters of Kronotek, an organization that has developed time travel technology and is apparently dedicated to the research and protection of history. Kronotek's senior management, known as "Mother", informs Morris that Dr. Koell, the organization's founder, has gone missing and history has begun to experience unrest, putting people who played key roles in history in danger, and instructs Morris to help Kronotek restore history.