This is a long one, so check out the full poem here.
Our speaker starts off with a poetic description (what other kind of description would you expect?) of the Ozark Mountains. More specifically, the description is of the land at the base of those mountains, where you can find flowers, and prairies, and streams, and buffalo, and wolves, and vultures, and bears (oh my!).
It turns out that Gabriel's here, hunting with "Indian guides" (1008). Evangeline, Basil, and company are here too, always just behind Gabriel's party.
One night, "an Indian woman, whose features / Wore deep traces of sorrow" wanders into their camp (1017-1018). As it turns out, she's a member of the Shawnee tribe. She's returning from a hunting trip, on which her husband was murdered by a rival tribe: "the cruel Camanches" (1120).
They all have dinner together and then, after everyone turns in for the night, the Indian woman stays up to tell Evangeline the story of her love for her husband. Of course, Evangeline tells the woman her own sad tale. (It's a real pity party.)
The Indian woman then tells Evangeline the story of Mowis, who was made of snow: he fell in love and married a girl, but the day after their wedding he melted in the sunshine. (Are we sure this guy's name wasn't Frosty?) She also tells Evangeline about Lilinau, who was "wooed by a phantom" (1145) and, after following him into the forest, was never seen or heard from again. Evangeline wonders if she isn't in love with a phantom, herself.
The next morning, Evangeline's group moves on, with the Shawnee woman accompanying them and, eventually, telling them about a nearby Mission. Evangeline encourages the group to swing by the Mission, "for there good tidings await us!" (1171). They head in that direction and arrive at the place (it's a Jesuit mission to be specific) just after sunset. The group approaches and sees that everyone's in "evening devotions," so they all join in (1184).
Once the service ends, the priest welcomes the visitors and invites them into his "wigwam" (1190). He gives them some maize cakes and water (yum!), then reveals that Gabriel was just here—not six days ago. Bad news: he's headed far to the north. Good news: Gabriel plans on returning the Mission, once autumn arrives.
Evangeline asks to stay on with the priest until Gabriel returns. Basil, though, has… a life. He peaces out back to his home, while Evangeline stays behind.
Months roll by, and the priest keeps Evangeline's spirits up by reassuring her that Gabriel will return and by showing her religious symbols like "the compass-flower, that the finger of God has planted / Here in the houseless wild" (1219-1220).
Despite the priest's encouragement, Gabriel doesn't show up. Autumn ends, then winter, and then spring. In summer, a rumor emerges that Gabriel has a cabin up in Michigan so Evangeline leaves the mission and heads on up there, only to find the cabin deserted and in ruins. This is not going well for her.
After this disappointment, she moves on from place to place, getting older and more careworn with each passing year (sniff).