KronoteK has been founded to use their time-travel-technology to set things right with history - whatever that means. One thing's for sure: The player was one second away from losing his scalp to an Indian at Custer's Last Stand when KronoteK came by and snatched him. The reason: KronoteK themselves can't do anything themselves in order to keep the time-continuum safe. So they need persons marked MIA. People that as far as history is concerned are only a ghost. Of course, KronoteK isn't the only time-traveling-agency out there and soon after your first missions in the American Civil War and World War I, the problems suddenly get a lot bigger when well-equipped time-travelers enter the scene and mess everything up.
Darkest of Days is a first-person-shooter where the player and his tutor Dexter travel through different periods of time, including ancient times like the destruction of Pompey, to fulfill KronoteK's objectives. They blend in with the setting, using clothing and weapons fitting for each time period. Modern guns are introduced only when necessary to make things easier. However, not everyone can be killed on sight.
Important persons from history glow either golden or blue. Golden ones are mission-critical and must be saved at all costs. Blue ones can be taken out by shooting them or using special chasers that target blue-glowing enemies and eliminate them without disrupting the timeline. Killing a blue-glowing enemy will reduce the reward at the end, but not end the mission. The player's upgrades for their rifle and sidearm will also decrease in value.