313 AD, and tempers are rising in Rome. The Emperor Constantine and his mother Helena are trying to make sense of the new Christian religion which is spreading through the Empire - but the Christians can't agree among themselves. Scholars are locked in a bitter struggle over whether Christ really was the son of God, and Constantine invites delegates from both sides to debate before him at his villa.

Now strange things start to happen. Envoys from both sides are found murdered in a most macabre way. The villa is secretly attacked, and the Holy Sword is stolen. Helena calls on the help of her secret agent Claudia - that shrewd, unobtrusive detective - to untangle the dangerous web of intrigue. As she sets to work, the spy is also facing a crisis in her own life...