The Hero's Journey is a framework that scholar Joseph Campbell came up with that many myths and stories follow. Many storytellers and story-readers find it a useful way to look at tale. (That's actually putting it lightly. Some people are straight-up obsessed.) Chris Vogler adapted Campbell's 17 stages of a hero's journey, which many screenwriters use while making movies. Vogler condensed Campbell's 17 stages down to 12, which is what we're using. Check out a general explanation of the 12 stages.
The story of Io doesn't fit perfectly into the Hero's Journey structure, but we're giving it a shot. As the gross old saying goes, there's more than one way to skin a cat. Here's how we've diced up the story:
Yep, our heroine totally starts out in this phase of the Hero's journey. To the lovely naiad, "ordinary" is splashing in waters of her father, the river god Inachus, all day. She never even gets pruney fingers. That's just one of the many benefits of being a water nymph.
Call To Adventure
Io hits this phase when Zeus approaches her in the woods and tries to seduce her for the first time. This is a wee bit different than a lot of other heroes' journeys. It's not like Io is being called on to do anything all that positive. Helping Zeus cheat on his wife definitely won't win her any medals.
Refusal Of The Call
Being the good little naiad she is, Io totally refuses the call. She's like, "No way Zeus! I heard about how you treat the ladies, so get on back to Olympus." Too bad Zeus doesn't know how to no for an answer.
Meeting The Mentor
This phase only works if you think of Zeus as a seriously twisted mentor. Most of the time, the mentor figure helps the hero or heroine along in some way. Instead, Zeus traps Io in a bunch of clouds and either seduces her or forces himself on her, depending on the version of the story you read.
Crossing the Threshold
The threshold has been thoroughly crossed by the time Zeus's wife Hera busts onto the scene. When Zeus transforms Io into a white cow to hide her from his suspicious wife, there's no doubt that the Io is being forced to kiss the ordinary world she began in goodbye.
Tests, Allies, Enemies
Io's journey totally lines up with this step of the Hero's Journey. Hera gives the white cow to her henchman, Argus Panoptes, to guard. Sounds like it's pretty safe to say that that they fall in the enemy category. Zeus, however, helps her out by sending Hermes to lop off Argus' head. And there's your ally. Well, Zeus got her into this mess to begin with, so maybe he's kind of an enemy at the same time.
Approach to the Inmost Cave
The story of Io skips over this step. Instead of showing Io trying to rev up to some big challenge, the myth just jumps right to it.
Io faces her worst ordeal after Argus' death. (Wow, thanks a lot, Zeus and Hermes.) Hera is so ticked off that she sends a gadfly—or the Furies, depending on the version—to torment Io wherever she roams. The poor white cow stampedes all over the earth being constantly tortured.
Eventually, Io's suffering comes to an end. She gets to Egypt and moos so sadly about her fate that Zeus finally steps in. The king of the gods convinces his wife to chill out with the torture. Often in this stage, there's a transformation of some kind; the story of Io totally fits the bill when Zeus transforms her back into the lovely naiad.
The Road Back
Nope, Io never returns to the ordinary world to face more dangers like some heroes do. Instead, she chills in Egypt.
This is supposed to be the place where the hero or heroine faces their biggest danger, but Io has already done all that.
Return With The Elixir
Though Io never returns home, she does get a reward in the end. Not only does she get to stay in her beautiful naiad form, she eventually becomes worshipped in Egypt as the goddess, Isis. Later on, though, her descendants Cadmus and Danaus do return to Greece, so you might say that they complete this part of Io's hero's journey on her behalf.