The syndicated sex-advice columnist Dan Savage has a rule — one among many he’s compiled in his years in the business — for identifying bogus questions that show up in his mailbox. It’s one that novelists would be smart to note. It boils down to this: If the prose reads as if it were a letter to Penthouse, the writer is lying, and lying badly.

Jess Winfield, in his comic novel, “My Name Is Will: A Novel of Sex, Drugs, and Shakespeare” (Twelve, 291 pages, $23.99), writes sex scenes that Mr. Savage would reject out of hand. So will readers, and this is a problem because, as the subtitle suggests, sex plays no small role in the story he has to tell.

In fact, he is telling two stories in alternating chapters, one lively, smart, and mature, the other sloppy and sophomoric, seemingly the work of a writer much younger than Mr. Winfield, who has been a grown-up, and a professional writer, for some time now. “My Name Is Will” is a debut novel, but only half of it feels that way.

Unfortunately, it is with this half that the book begins. First line: “Willie sat in the back row of a blocky white minibus, his hand cupped around the enormous psychedelic mushroom hidden under a denim jacket laid too casually across his lap.” Before the paragraph is over, there’s a crude reference to Queen Elizabeth I’s left breast. Farther down the page, things get a bit more vulgar, as if to make unambiguous that Mr. Winfield’s target audience is male, puerile, and into sex, drugs, and Shakespeare. (Is this, one wonders, a sizeable demographic?)

Willie is William Shakespeare Greenberg, so named by his mother, who had great hopes for him. But his mother is long dead, and he is a 25-year-old slacker at the University of California, Santa Cruz, too busy smoking hash and hunting for mushrooms to come up with a coherent topic for his master’s thesis on Shakespeare. In desperation, he hits on the notion of proving, through Shakespeare’s text, that the Bard was a secret Catholic in an era of bloody persecution of papists. The year is 1986.

Cut to 1582, when William Shakespeare is an 18-year-old, semi-incompetent Latin teacher in Stratford-upon-Avon, keeping his students in check with the kind of bawdy, punning insults that he would later write into his plays. From the start of Chapter 2, the tone is entirely, even bracingly different from the 20th-century tale, and William is utterly convincing as a character: callow and a bit lost, but witty and kind, and fully possessed of the ability to charm or flay with words. He is just as lascivious as Willie, if not more so, but he at least has some sweetness about him. When Willie wants to bed a woman, which is often, he quotes Shakespeare.

The challenge Mr. Winfield has set for himself is to bind these stories to each other, employing psychedelic, time-travel echoes to make them symmetrical without making them the same. But Willie’s story, which takes him on a road trip to Berkeley and a Renaissance fair, and includes repeated encounters with a theater troupe called Short Sharp Shakespeare, has far more echoes of Mr. Winfield’s life than of the Bard’s. (An attempt to equate Drug Enforcement Administration operatives who pursue drug dealers in 1986 with representatives of the Crown who hunt down Catholics and have them drawn and quartered in 1582 is particularly forced and embarrassingly lame.)

Mr. Winfield, who went to school at both Santa Cruz and Berkeley, co-founded the Reduced Shakespeare Company in 1981. The troupe played Renaissance fairs and found fame with its breakout hit, “The Complete Works of William Shakespeare (abridged),” at the 1987 Edinburgh Festival Fringe. Willie’s half of the novel has the distinct feel of a roman à clef — and of film-deal bait, the 16th century not being as popular with teenage boys as Hollywood might like (and Mr. Winfield being a former writer and producer for the Walt Disney Company).

It’s in the chapters on Shakespeare, which are not aimed exclusively at drug-addled, Bard-loving lad-mag readers, that the book comes to life with intelligence, humor, and high stakes. This story line proves Willie’s almost inadvertent acuity, making a fictional case for the playwright’s Catholicism — an argument that, a character in the novel notes, has indeed been made in scholarly circles. As Mr. Winfield explains in his afterword, the events he relates from Shakespeare’s youth “are a pastiche of fact, legend, and surmise”; though he certainly knows his stuff, he isn’t writing history here. He wanted, he says, “to tell a ripping yarn,” and that he does, at least in this half of the book.

Along the way, he allies himself quietly but staunchly with those who believe William Shakespeare was, indeed, William Shakespeare — that this man, though not noble, had the knowledge, the education, and the life experience to write the plays that bear his name.