The episode comes from the Apocryphal book of Tobit. The elderly and blind Tobit, sensing he was near death, sent his son Tobias from Nineveh to Media to collect a debt. He was accompanied by the archangel Raphael; during the journey Tobias caught a fish whose gall, Raphael told him, would cure Tobit’s blindness. The drawing shows the arrival at their destination of the angel and Tobias, trailing the fish. Cat. 17