The plot centers around a Grail War faultily copied from the Third Holy Grail War in Fuyuki. After the end of the third Grail War, an organization from the United States that has magi separate from the London based Mage Association as members took data from Fuyuki's Grail War and planned their own ritual. After seventy years, they used the city Snowfield as the Sacred Land for their own Grail War. They were unable to successfully copy every aspect of the ritual, which lead to it acting only as an imitation that has lost the Saber class and allowed for the summoning of strange Servants due to the definition of a "hero" being blurred.

A Fate/Zero oneshot from the first TYPE-MOON Ace, following Emiya Kiritsugu as he bids farewell to Illya before leaving for Japan’s 4th Holy Grail War, while Irisviel and Saber observe and discuss him.

The stage: the city of Snowfield in the western U.S., far from Fuyuki. There, a "false Holy Grail War", quite unlike the original Holy Grail War, unfolds. There were those who had been keeping an eye on the auguries of the Holy Grail in Snowfield. According to an investigation by the Mage's Association, the Holy Grail War system in Snowfield was an imitation of the one in Fuyuki. What's more, the system was incomplete, leading to the exclusion of one of the seven classes and the selection of beings as Servants who ordinarily could not be summoned. It was, verily, a strange fake. As an organ of the U.S. government executes its various plots, the Servants are summoned one after another...