The story concerns a young American geologist, Stanton Laird, working in the Australian outback in the field of oil exploration. Although he is in a very remote location - beyond the black stump - in a region called "the Lunatic" in Western Australia, he is part of a crew that has a well-appointed mobile facility.

He is befriended by a local farming family, the Regans, and develops a relationship with their daughter Mollie. The Regans run an enormously profitable station, but their domestic lifestyle is, to say the least, unconventional, with the two Regan brothers at one time having Mollie's mother move from one to the other without bothering to get a divorce. The family is large, and even larger when counting the half-caste children produced by both fathers, and the children are taught by the Judge, an English exile and alcoholic, who gives the children an excellent education and keeps the finances of the station properly accounted for. Over the course of the explorations (which prove unsuccessful), he notes the unique lifestyle on what amounts to the Australian frontier, and falls in love with Mollie. The two wish to wed, but Mollie's mother insists that Mollie first see how the Lairds live in their Oregon town, Hazel, which was once on the frontier, but is no longer, though its citizens take pride in feeling that it still is.

The two travel to Hazel. At first, Mollie gets along well in the Laird family home. But then Stanton's one-time love, Ruth, the widow of Stanton's best friend, returns to Hazel with her son. The son bears a tremendous resemblance to Stanton, and Stanton is moved to confess to Mollie both that the son may be his, and that he killed a girl in a drunken accident as a teenager. Mollie is unconcerned about the boy—such things are common where she comes from—but is concerned and judgmental about the accident, and about Stanton's lack of concern for the dead girl. As Stanton expected Mollie to care very much about the boy, and did not expect her to be so concerned about the girl, the two begin to realize they have a very different outlook on life.

Eventually, Mollie comes to realize that she will never fit in while in Hazel, and does not particularly want to. Her place is on the true frontier, in the Lunatic, not in Hazel. She returns to Australia, where she will likely marry a young neighbor, an emigrant from England, who has long loved her. Stanton is likely to marry Ruth, as Mollie suggests he should. Stanton has a wedding present for Mollie, though—his final report reveals that the neighbor's impoverished lands lie over great quantities of artesian water, which will allow the neighbor—and Mollie—to flourish.