The Western Roman Empire is falling; and after a set of lengthy philosophical debates with himself on Whether the End Justifies the Means, Aziraphale decides to take matters into his own hands.

Meanwhile, in the brazen luxury of Constantinopolis, Crowley struggles with the biggest personal crisis any demon has ever suffered - which would be difficult enough, even without the Emperor's new Christian priest nosing after him.

When their conflicting assignments put them on the opposite sides of the same battle, Crowley remembers an act of kindness left unreciprocated since Sodom and Gomorrah; and what had started off as an angel-hunt transforms into something far less defined.

Because Crawly is dead; and Crowley has changed.