The Milieu Story The whole point of the story is to discover this strange, new world.
Arrival - A Stranger from the outside arrives (by purpose or accident); he is unwelcomed and imprisoned, but gradually proves his worthiness.
Initiation - Stranger is formally welcomed into the society; taught the culture & language; shown sharp contrast between stranger’s world and present one which challenges the stranger’s own belief system.
Departure - Stranger rejects or is torn away from society, & returns home with greater self awareness.
Notes:
Milieu stories always follow the same structure. A stranger who will see things as we would see them is somehow shipwrecked or stranded or lands in the strange place, sees all the things that are interesting, is transformed by what he sees, and then goes back home a new man.
The Stranger is the viewpoint character. The Milieu is seen through his eyes, since he will be surprised by and interested in the same strange and marvelous (and terrible) things that surprise and interest the audience. Remember: The whole point of the story is to discover this tranger, new world, and what better way than through the eyes of a stranger to the world.
In Pierre Bolle's Planet of the Apes, the story begins when Astronaut Ulysse Merou is stranded in a world in which apes (and not humans) have evolved as the dominant sentient species, and ends when he leaves. He is transformed by his experiences on the Monkey Planet, but he does not stay--and attempts to return home. Other stories are told along the way, but however much we care about those events, the closure we expect at the end of the story is the main character’s departure from the Monkey Planet.