[2] In the first novel, Fireball, Simon and Brad are cousins who are mysteriously transported to an alternate history Earth, where the Roman Empire did not break up and Europe remains in pre-Dark Ages technology.

In an attempt to improve their status in the new realm, Simon and Brad aid the Christian Church, which is oppressed, to launch a coup by introducing the stirrup and the longbow.

Brad, Simon, and their companions Bos and Curtius are greeted warmly by the Vikings and believe they can live here permanently, only to realize that they are to be sacrificed.

As the Roman Empire has persisted in Europe of this realm until the 20th century due to unchanging conditions, the Aztec civilization too has continued without encounters from the Europeans' discovery of the New World.

In order to quickly gain wealth and status to enjoy a comfortable living, they take part in the sacred games, which is a cross between squash, tennis and handball.