[1] Setting: Hungary in the year 1213 King Endre II, the monarch of the country, is fighting abroad while Gertrude, his queen, who is of Meranian birth, plays hostess to the leading members of the Court (in the first place foreigners) at prodigal feasts.

A group of angry Magyar nobles headed by Bán Petur are plotting a conspiracy against the queen, anxious for the fate of their homeland and the honour of Bánk's wife.

It is revealed that Tiborc, a vassal of the Bán, saved his life at a battle long ago; Bánk promises his aid.

In his bitter grief Bánk blasts a terrible curse at his own son, but then raises to himself the innocent little boy, giving solace to his wife.

Finally, he asks Tiborc to escort Melinda and their little son to their home, a castle in East Hungary, beyond the River Tisza.

In the throne-room Bánk calls the Queen to account for plunging the country into poverty and for the honour of his betrayed wife.