Inachus, the river god, was deep in sorrow.
"My beloved daughter, Io, has vanished. Until she is found, I will never be content to release the waters under my rule."
What he did not know was that Io had been combing her hair in the meadow when suddenly a bearded man began to chase her. Shocked, Io took flight and tried to escape, but the stranger caught up and forced her to submit to him.
Juno, queen of Olympus, was searching for her husband Jupiter. A small, wispy trail of mist caught her attention.
"If I am not wrong, my husband has forced himself upon another maiden. I will force him to reveal himself."
Under her orders, Iris cleared away the mist. But when Juno finally confronted her husband, he was holding not a girl, but a large white cow.
"What is the meaning of this? Why are you embracing a simple heifer? Have you grown so desperate?"
"It is nothing, my dear wife. I wanted only to admire this heifer. Look at its beautiful white coat. Have you ever seen such a thing?"
In fact, the cow looked too perfect. Just as Juno began to descend from Olympus, Jupiter had used his power to transform Io.
"May I have the cow, dear husband? Only the queen of the gods should possess such a wonderful heifer."
Jupiter realized he had no choice. "Very well. It is yours."
Putting a rope around its neck, Juno led the cow to her private garden. There, she summoned Argus, the watchman of Olympus whose hundred eyes saw everything around him for miles. "Watch this cow. Do not let it leave."
"As you wish, Juno."
Under Argus's watchful gaze, Io tried desperately to adjust to her new body. Walking on four legs and swinging a tail proved tiring and her new horns weighed down her head. Each day, she had only an hour to wander, and her only food was grass. Whenever Argus was thirsty, he would pick her up and milk her udder dry. If he decided to nap, he would tie her to the nearest tree and take care to ensure that the knot was as tight as he could make it. Poor Io was miserable, but she could do nothing to change her fate.
Looking down from Olympus, Jupiter felt nothing but pity for the girl he had left to suffer.
"Mercury, go and free that cow. Do whatever you must."
Dressed in the robes of a shepherd and leading a large flock of sheep, Mercury approached Argus.
"Fair giant, I am in need of grass for my sheep. Will you be so kind as to let them graze?"
"Very well. But leave as soon as you are finished."
Sitting on a large rock, Mercury took out his pipes and began to tell a long and dull myth about the god Pan. In between, he played a beautiful, soothing tune. Argus, exhausted by the strain of keeping all his eyes open, let half of them close. Despite his strongest efforts, the rest soon shut as well.
Seizing the chance, Mercury placed a spell of eternal sleep on each eye. Without his eyes to awake him, Argus suffocated on his own drool.
As soon as Mercury untied her, Io ran as fast as she could to her father Inachus. She tried to speak, but made only loud moos.
"Why are you bothering me, cow? Unless you know where my dear Io is, leave me in peace."
Feeling the soft sand beneath her hooves, Io tried writing her name in large letters. Inachus finally understood what she wished to tell him.
"Is it true? Are you my daughter?"
"Io, what has happened! You were a fine maiden when last I saw you, and now you are a heifer! I had hoped that you would marry soon, so that I would have grandchildren, but now you will have to mate with a bull. My descendants will be cattle!"
As he and his daughter wept, Jupiter could hold his rage in no longer and stormed into Juno's chamber.
"Look what you have done, my dear wife! The girl will spend the rest of her days as a cow, never finding peace. Release her at once!"
Juno went to find Argus, but instead found only his corpse, preserved by Mercury's spell.
"My faithful servant! Your service will never be forgotten. I will place your eyes upon my peacocks, so that they may be seen by all who look at them. And that foul cow! She will pay!"
Io was grazing when a large gadfly stung her from behind. Unable to escape her attacker, she began running wild across Greece and Egypt. Her father, Inachus, asked his master Neptune for help. Before any more chaos could be stirred up, Jupiter killed the fly with a thunderbolt. Having led Io back to her home, he gradually undid her curse. Io's horns and hair fell off, her udder shriveled to a tiny speck, her body shrunk back to its normal size, and her face was restored. As she found herself standing upon two legs again and able to speak words, she suddenly realized she was naked. Jupiter wrapped her in a beautiful dress of linen and brought her to Olympus, where she was given immortality and made a minor goddess under Juno. Since then, she and her son Epaphus have reigned, having finally found a measure of peace.