Bill Masters is a sex researcher who admittedly doesn't know very much about sex. In one of the very first scenes of Showtime's excellent scripted drama "Masters of Sex" (Sunday at 10), which chronicles the pioneering real-life work of Masters and Virginia Johnson, Masters is puzzled to learn of the very idea of women faking an orgasm, and tries to press a prostitute named Betty for an explanation as to why she would practice such deception.

Betty, who doesn't have Masters' book learning but understands this particular subject with far more depth and breadth, rolls her eyes and tells him,  "If you really want to learn about sex, then you're going to have to get yourself a female partner."

It's a line, like so much of "Masters of Sex," with a double meaning. Does Betty want Masters to find a woman to help him study and understand sex, or simply find a woman to have sex with? And in the end, Masters gets a partner — former nightclub singer Johnson — who's excellent at the former, but whom he would very obviously like to try at the latter.

Created by Michelle Ashford, adapting the Masters and Johnson biography of the same name by Thomas Maier, "Masters of Sex" is the best new show of the fall by a very long stretch. It's also a refreshing anomaly: a prestige cable drama that doesn't feel like a recombination of elements from 15 shows that came before it. It's not another Bastard Son of Tony Soprano like "Ray Donovan" and "Low Winter Sun," and even though it begins in the late 1950s, the only resemblance to "Mad Men" involves the clothes and the quality.

Michael Sheen and Lizzy Caplan are terrific in the tonally opposite lead roles. Masters is cultured and prestigious; Johnson is working class. Masters is guarded and opaque; Johnson is an open book. (When she takes on one of Masters' colleagues as a lover, she warns him upfront that it will not become a romantic relationship.) He's a man very much of his time; she's an evolutionary leap forward.

We open in 1956 with Masters' research at the earliest of stages — he cuts out early from a rubber chicken dinner so he can watch through a hole in the wall as Betty satisfies her clients (but never herself) — at Washington University in St. Louis. He wants to take sex out of the shadows and into the light; as he tells mentor Barton Scully (Beau Bridges) in a later episode's flashback, "Humans have taken the basic impulse for sex and turned into some unrecognizable ordeal... What if we could just cut through the maze to the essentials?"

We get a sense that this is more than just professional curiosity for Masters. Betty (Annaleigh Ashford), one of the series' more astute, blunt characters, suggests he likes to watch, and his sex life with wife Libby (Caitlin FitzGerald) is clinical and distant; when she offers to let him watch her pleasure herself for the sake of the study, he tells her, "I love you too much." (That Libby also calls him "daddy" does not help.)

Johnson, meanwhile, is a woman ahead of her time, a single mom eager for the professional challenges — and, yes, money — offered by working for Masters, and acutely aware of the effect she has on him and how she can take advantage of that while still advancing the study. It's a constant battle for power between the man of science and the woman of instinct, and the constantly shifting ground between them keeps "Masters" exciting.

What's perhaps most impressive about "Masters of Sex" is how sincere it is. So many shows about sex take on a cheeky tone, or a self-congratulatory one. This one features an abundance of nudity — nipple fetishists in particular will have never had it so good — and a healthy amount of simulated sex and masturbation, yet there's never a sense that we're meant to giggle at this, nor that Ashford and the rest of the creative team are patting themselves on the back for their daring. It can be a very funny show at times — among the early highlights is a subplot about a handsome doctor who falls for his partner in the study, even though she won't have sex with him away from the watchful eye of Dr. Masters — but it's also matter-of-fact about all the body parts and all the thrusting. You make a show about wiseguys, you have to include some violence; you make a show about sex researchers, and you have to show a lot of sex.

Much of that certain, straightforward tone is established in the pilot by director John Madden ("Shakespeare in Love"), who has an instant command of the period, the subject matter, and, especially, his two stars. This is far outside what Caplan's usually asked to do, but she doesn't come across as an anachronism (Virginia's not like the other secretaries at the hospital, but she's also not a time-traveler), and she does a lot of sly, subtle work as we see Virginia try to figure out her mysterious new boss. And Sheen is simply superb as the icy Masters, forever at war with himself over his desire to help others and his need to control every situation and relationship. There's some fairly trite storytelling at times regarding Masters' abusive father (even a relatively novel cable drama's hero has to have daddy issues), but Sheen sells it for everything it's worth.

One of the reasons we've had so many violent anti-hero dramas over the last 15 years is that the business imitates success, and everyone's still chasing "The Sopranos." But another is that violence makes it easy to create emotional stakes. What's so impressive about "Masters of Sex" is how powerful it can be without once involving guns, fists or exploding tortoises. There's a scene in the sixth episode, involving Allison Janney as Scully's wife, that is among the more devastating moments you're going to see on TV this year outside of "Breaking Bad," and all the drama and tears stem from societal expectations and the intimate, specific details of a marriage.

Showtime hasn't been on the best creative streak of late. "Homeland" had a shaky second season. "Dexter" had a weak final season and a disastrous last episode. "Ray Donovan" got through an entire first season without providing a single character worth caring about.

But the first two episodes of "Homeland" season 3 are promising, and "Masters of Sex" is even better than that.

Alan Sepinwall may be reached at sepinwall@hitfix.com