Altar of the Falsehood/Lie. According to saintpeterbasilica.org:
This altarpiece is a mosaic work representing The Punishment of the Couple Ananias and Saphira, from the original painting Cristoforo Roncalli (known as the "Pomarancio" of 1604.
After lying to St Peter, Saphira fell to the ground before the Apostle; in the background two young men carry the dead body of her husband, Ananias.
Acts 5:1-11