Circe and Scylla. To find out more about the rivalry between Circe and Scylla, see this Wikipedia article: link; for information about the image: image source.
This painting shows a famous story from Ovid's Metamorphoses, in which Circe (the famous witch of Homer's Odyssey) is in love with Glaucus, a sea god - and so is Scylla, a water nymph. Circe is a dangerous person to cross! What you see here is Circe, in the foreground, pouring poison into a stream where Scylla liked to bathe; you can see the lovely Scylla in the background. Once Scylla plunged into the water, she was turned into the monstrous Scylla that you know from the twin perils of "Scylla and Charybdis."