Metamorphoses Book 1: Io
Io, daughter of the river Inachus, caught Jove's eye one day as she was returning from her father's stream. When Jove descended to possess her, she ran into the forest. Although he told her who he was, she wouldn't stop running, so he covered the earth in darkness so that she wouldn't be able to run away from him. In the artificial night, he ravished Io.
Juno, Jove's wife and sister, noticed the fake night that darkened earth and knew that her husband was up to something, so she descended from Olympus and dispersed the clouds. Jove turned Io into a white heifer so that he wouldn't be caught in his infidelity. Juno, though suspicious, couldn't help but admire the beautiful animal, and she asked for it as a gift. Knowing that if he refused to give the heifer to his wife she would become suspicious, Jove agreed. Juno gave the heifer to Argus, a man with a hundred eyes, to keep watch over her. Day and night Argus watched over Io and she was miserable in her new form. During the day when she was allowed to graze she wandered to her father's stream and there she followed him and her sisters, but none recognized her until she scratched her name into the dirt with her hoof. Her father was distraught at the fate of his daughter, and Argus separated the family. He took Io to a distant field where he could sit on a mountaintop and guard her. Jove felt sorry for Io, and so he sent his son, Mercury, to kill Argus.
Mercury descended to Earth and wore a shepherd's disguise. He played a pipe so enchanting that Argus invited the stranger to share the shade with him. Mercury sat with Argus for hours and told stories and played soothing music on the reed pipe to lull the guard to sleep, but although many of the eyes closed, Argus managed to keep a few eyes open to watch Io.
Argus asked where the reed pipe had come from because he'd never seen one before, and so Mercury told him the story of how Pan fell in love with a Naiad named Syrinx. Syrinx was a chaste nymph who was often mistaken for Diana, the goddess of the hunt, because she was also a beautiful and chaste huntress. Pan saw her and desired her, but she ran away from him. She was running through the woods when she came to a river, and she begged her sisters, the water nymphs, to change her from her human form so that she could escape Pan. When Pan reached her, she had been changed into marsh reeds, and he sighed out his disappointment. The sigh played through the reeds like a song, and so Pan waxed together reeds of different length and made a pipe that bears the name syrinx after the Naiad he lost.
Argus had fallen asleep before Mercury made it through the story, so the god sealed his sleep and then lopped off his head. Juno took Argus' eyes and put them into the feathers of her bird, the peacock. She was furious, and so to get revenge against Io, her rival, she put a spell of madness on the heifer. Io ran around the world terrified until she came to the banks of the Nile. She grieved so deeply that Jove begged his wife to remove the spell. He swore on the river Styx that he would not be unfaithful with Io again. Juno was satisfied, and so she returned Io to her human form. Io became a goddess and bore a son named Epaphus from the seed of Jove.