Its title comes from French "Le bon roi Dagobert" nursery rhyme,[1][2] and though the cast contains historical characters the plot is fiction.

Dagobert, the dim, dirty, idle, cowardly and lecherous king of the Franks, is under pressure from his ministers and the Roman Catholic church to make his peace with Pope Honorius I.

He undertakes a pilgrimage to Rome, seeking both an alliance and absolution for his countless sins.

Repeatedly outwitted there by far wilier men and women, he returns home with a poisoned brooch for his queen, his plan being to remove her and marry an alleged daughter of the Byzantine emperor Heraclius.

His ministers arrange for his corpse to be hauled into the sky at night from a high tower and then proclaim that he had ascended into heaven.