Although William Buckley Jr. began his long recessional from public life some time ago, the imaginative richness of his later work is second only to the fecund prime that gave shape and coherence to modern American conservatism. His commentary has lately seemed reinvigorated, its creativity more concentrated, and its critical deliberations more thoughtful.

Aside from his syndicated column and the odd public audience, these energies have been directed into fiction: Six of his last seven books have been novels. As a novelist, Mr. Buckley is best known for the espionage adventures of Blackford Oakes, but he has also created another world that transmutes his own experience into the realm of the novel. Historical and fictional characters blur in and out, including Mr. Buckley himself. “Getting It Right” (2004) surveyed the turbulent early days of the conservative movement, while “Redhunter” (1999) sorted through the mind of Joseph McCarthy, and so forth. Austin Bramwell, a former trustee of National Review, calls these books Buckley’s “American novels.” Each alludes to the others and forms a coherent whole, saying something large about American history that’s also intimate.

Mr. Buckley’s new novel, “The Rake” (Harper Collins, 278 pages, $24.95), would seem to join with the American novels. But it is more its own discrete work, quite unlike anything Mr. Buckley has written before. Most astonishing is the language, from which Mr. Buckley has scraped away his characteristically ornate formulations. The prose is minimalist, even austere, achieving its power through silences, compression, and deep suggestion.

“The Rake” opens in 1969, at a university in North Dakota. Reuben Castle is the student-body president, the editor of the campus newspaper, and “in a hurry for something else.” Castle is attempting to seduce the deeply religious bluestocking Henrietta Leborcier. One evening she finally relents, in a duck blind, with “a shaft of fear, and the dull pain of sin coveted, and acquiesced in.” The affair results in a pregnancy, and Henri extracts a submission from Castle: So that the child is not illegitimately born, the two are secretly wed.

Shortly afterward Castle abandons Henri, and they careen off in separate directions. Time in “The Rake” turns back and forth in intricate whorls, glimpsing into the lives of father, mother, and son. Castle dodges the draft and espouses all the fashionable causes of the era. Soon he is a leading light in the political firmament. By 1992, just as he is about to acquire the Democratic presidential nomination, his secret history begins to emerge, and he makes ever more monstrous choices to protect himself.

Castle is a thoroughly loathsome figure — deceiving and self-deceiving, buffoonishly “progressive,” and a serial philanderer, perpetually in search of openings that “increase the prospects of success, while diminishing the pains of achieving it.” No doubt correspondences will be drawn to another skilled provincial politician who sought the presidency in 1992. Yet while Castle as a President Clinton manqué is plausible enough, in context the correspondences are strained.

Under the usual conventions of American political fiction, the protagonists are corrupted by the political world. Mr. Buckley’s vision is different. Castle does not lose his innocence; he never had it in the first place. He enters into the political world precisely for that reason. For that matter so does every other political actor in “The Rake.” The book, then, is not particularly political in any partisan sense. Castle seems not to represent this or that politician but all of them — the every-politician: “Probably the thing to do was to act absolutely natural,” Mr. Buckley writes. “He had this difficulty, which many first-rate politicians caught up in the theater of politics have, namely that he wasn’t sure what was in fact natural.”

Compared with the American novels, there is a shift in Buckley’s perspective: more melancholy, more ominous, like a change in the light at dusk, which colors his tone and subject. “The Rake” is a view of American politics as a sinister moral wasteland, sharpened by references to Castle as “conspicuously American” or “an American rake.” From Mr. Buckley, who spent a half-century in the thick of the political scene, such disillusionment is striking.

Without giving away too much, “The Rake,” ostensibly political fiction, gestures beyond politics. It is an expression of a late style, of experience distilled by the passage of time: the loss of old certainties, the formation of character, irrevocable human choices, all the while alluding to questions that try our understanding and ultimately remain elusive. In the entwined lives of “The Rake,” Mr. Buckley, now nearly 82, has given us perhaps his last gift — a penetrating meditation on change, complication , and life’s contingency.

Mr. Rago is an editorial page writer at the Wall Street Journal.