In a world influenced by ancient Rome, but still very far in the future, seventh born sons are valued for their enhanced abilities or talents (telepathy and telekinesis). The reverence goes so far as to merit an esteemed position in government second only to the High King.
So, when a seventh son of a seventh son is born, it is almost assured he will someday hold the honored position of Sept Son. As such, Hadrian's future is almost completely assured from birth. However, being a member of the minority of Almighty worshipers, his time in office is also guaranteed to be fractious.
Zezilia was the disappointment. First born daughter after six sons, she was supposed to be the seventh son to restore her family's honor. Instead, she is left to salvage the disastrous situation by marrying well and producing a seventh son instead. That is until a stranger appears and declares her destined for an entirely new journey.