A conservative and enigmatic American cardinal, Lenny Belardo, is unexpectedly elected as Pope Pius XIII, becoming the first American pontiff in history. Behind a carefully cultivated air of mystery and an iron theological conservatism, he proves to be a deeply contradictory figure — demanding absolute devotion whilst harbouring profound personal doubts about his own faith. As he manoeuvres through Vatican politics and clashes with those who hoped he would be a malleable figurehead, his unconventional methods and psychological complexity reshape the institution around him.