The story is "The Treasure on Grafenberg" and apparently is the tale of a chimney sweep who was promised (by a virgin he happened to meet) untold riches if he would knock a frog out of a niche in a wall in a vault. When touched, the frog grew. Its eyes sprayed fire. The man jumped away and found himself back where her started. It doesn't say what happened to the woman.
Scott No.: 538
Date of Issue: December 6, 1973
Species: Edible Frog (Rana esculenta)
See also: First Day Cover, Maximum Cards
Scott No.: 908
Date of Issue: June 5, 1989
Species: European Tree Frog (Hyla arborea)
See also: First Day Cover, Maximum Card
Scott No.: 1609
Date of Issue: June 2, 2014
Set: Amphibians
Species: Yellow-bellied Toad (Bombina variegata)