“Some of the following is based on fact,” a coy pre-credit disclaimer notes at the beginning of “Bernard and Doris,” which makes its debut tomorrow at 8 p.m. on HBO, and “some of it is not.”

That much, at least, is true. As history, “Bernard and Doris” is utter bunk. Screenwriter Hugh Costello could have crafted a broad biographical tapestry depicting the life, marriages, scandals, and death of the real-life globe-trotting tobacco heiress, philanthropist, art collector, and sybarite Doris Duke. Instead, he has staked out the incidental real estate around a single relationship in Duke’s life and fabricated a sturdily imagined and intimate two-person drama.

Mr. Costello’s version of the Doris Duke saga picks up sometime in the 1980s as a divorced and childless Doris (Susan Sarandon) is entering late life. Ensconced much of the year in a massive New Jersey estate, she literally lives in a world of her own, penny-pinching, capriciously firing servants, and obsessing over a vast hothouse full of orchids. “Money has been an issue my entire f—ing life,” she howls at one point. But the real issue for Doris isn’t so much the money — inherited millions that she spends, invests, and charitably gives away — as the trust her millions can’t seem to buy.

When one of those ad hoc domestic exits brings a new butler to her breakfast table, Doris puts the man, Lafferty (first name Bernard and played by Ralph Fiennes), through the wringer. A veteran of such celebrity clients as Elizabeth Taylor and Peggy Lee, Lafferty proves up to the tasks that Doris sends his way like boulders in a landslide. He authoritatively rides herd on the rest of the help, attends to or tactfully overlooks Doris’s personal affairs — including a tattooed and dreadlocked musician boy toy — and, best of all, has a green thumb.

Slowly but surely, co-dependency flowers along with the orchids. What’s in it for Doris is the small but very necessary boost of tranquility she gets from having someone around to survey and organize the turbulent mixture of impulse and obligation that defines her existence. For his part, Lafferty gets a corresponding relief. He’s uptight, closeted, and clinging to white-knuckled sobriety, so administering to Doris’s global free-spiritedness and enabling her chronic alcoholism proves to be a spiritual balm for the butler. Encouraged to lighten up, Lafferty trades in his suit for slacks, lets his hair grow, and tries his hand at dating via a “men seeking men” classified ad in the Village Voice. Meanwhile, Doris has seemingly and at long last found a soul mate — someone who can tolerate her habits and quirks, keep up with her wanderlust, and never presume to penetrate her unflappable, acutely self-medicated mantle.

“We only have now,” Doris, who is never very far from a glass of sherry or an Eastern philosophical homily, tells Lafferty, now grown into a confidant and travel companion. True and false. Doris also has umpteen million bucks in the bank and, as Lafferty’s taste of the good life becomes something of a binge, just who has and who wants what from whom drags those trust issues back into focus. But Bernard is far too needy to settle for mere gold digging. As age slows Doris down, Lafferty’s role and his degree of control change. But their love, as neurotic and potentially toxic as it is, remains.

Despite the familiar dramatic territory, Ms. Sarandon and Mr. Fiennes are never stranded in cliché for very long. Mr. Costello’s unrepentantly episodic script gives them both plenty to work with. As Doris, Ms. Sarandon wields her voluptuousness and distinctive nasal sigh with vigor and grace. Mr. Fiennes has blessed his character with an Irish brogue that hones understatement to knife-edge sharpness just like the real thing. Tasked with having to play drunk for much of the film, a challenge that inclines many otherwise able performers to indulge in phony vocal and physical gestures, both actors ably rise to the dissolute occasion. A scene in which Lafferty serves a poached salmon while pickled to the gills will bring a shudder to any grown children of alcoholics scarred by booze-addled family meals.

Actor and sometime director Bob Balaban takes the thespian behind-the-camera high road and sensibly and unobtrusively documents what is essentially a series of two-person drawing room conversations that are only occasionally taken outside or complicated by the presence of additional characters. His camera endlessly tracks right or left in search of the next scene with curiosity rather than impatience. As a result, the film remains keenly in tune with its stars’ performances and takes its cues from the drama and pathos they conjure, not from the director’s ego.

Barring an opening flash-forward to the film’s conclusion that smells suspiciously of cutting-room re-jiggering, Mr. Costello’s script ably unifies numerous chronological nips and tucks using character portraiture of such insight and realism that it borders on the devious. What a shame, then, that the filmmakers have chosen to fill almost every passive-aggressive confrontation and non-confrontation with an omnipresent and insistent music score. “Bernard and Doris” so completely jettisons actual history in favor of tangible emotion through lines and character needs that quibbling about accuracy is irrelevant. It may be a completely inauthentic factual chronicle, but the film is nevertheless a small-scale storytelling tour de force for nearly everyone involved.