In A.D. 117, the Roman Empire is at the height of its power. Emperor Trajan has pushed its borders to their furthest extent with his recent conquest of the kingdom of Dacia, in what is now modern-day Romania.

What the Romans do not know is that this conquest has come at a terrible price. People across the new province begin to disappear, with villages, towns and entire cohorts of Roman troops vanishing into a dense, shroud-like fog that smothers the land.

Veteran cavalryman Tiberius Claudius Maximus has been sent by the new emperor Hadrian to assess any threat to the province. What he discovers is a force of evil entirely new to the world being born in the Dacian mists. If the Romans cannot correct their mistake and defeat this evil, it will wash across the empire and all of humanity, bringing with it an age of eternal night. ​