Toni Collette juggles identities in a new Showtime series.

Showtime’s two creepy-guy series, “Californication” (sex addict) and “Dexter” (serial killer), finished their seasons in December, making way for a trio of troubled-women shows - a new series and new seasons of two existing series - that begin this Sunday. In the premičre of “The L Word” ’s sixth and final season, the body of Jenny, a writer whose turn toward lesbianism provided the original story line of the show, is pulled from a swimming pool, and some of her friends are under suspicion; in “Secret Diary of a Call Girl,” a young woman in London leads a problematic double life as a regular gal and as a good-time gal; and in the new series, “United States of Tara,” Toni Collette plays a woman with dissociative identity disorder (the term now sanctioned by the American Psychiatric Association for what used to be called multiple personality disorder).

“United States of Tara” has a noteworthy parentage: it was created by Diablo Cody, who won an Academy Award for the screenplay of the hit movie “Juno” (along with a supersize Praise-and-Scorn Combo Platter from the press, for being an overnight success and for using that dumb name), and Steven Spielberg is one of its executive producers; Cody is also an executive producer, and wrote the first three episodes. “Juno” ’s story of a teenager’s pregnancy had an over-all affectlessness to it - you couldn’t tell whether you were supposed to think that the pregnancy was no big deal or whether its being no big deal was a comment on the kind of culture that leads to kids getting pregnant. The movie’s cool-loser-hipster tone gave it a tough skin. “Tara,” unlike “Juno,” is not a vacuum wrapped in an attitude inside a hoodie; and it benefits from having a central performer who, like Meryl Streep, has the ability both to disappear into a role and to persuade us that, whatever character she’s playing, she’s showing us her core. In “Tara,” Collette is a Kansas housewife who creates “opulent environments” for women with too much money on their hands; the mayor’s wife, Tara tells us, recently hired her to design “a seventeenth-century rococo nursery.” She says this in an introduction, which she is videotaping as she sits on a bed, and one might reasonably think, Oh, Lord, please, no. No characters filming themselves talking to the camera, please. But luckily the scene is soon over. “Tara” isn’t - yay! - clogged with self-consciousness; Tara films herself in order to keep track of her life, and remember where she left off, so to speak, when one of her other identities - one of her “alters” - takes over.

What makes “Tara” unusual is that D.I.D. isn’t treated as frightening and isolating, as a medical conundrum, or as the shortest route to laughs. Tara’s alternate identities are accepted by her family and by the community, and, in a way, she’s just the town eccentric. There are three distinct alters, all of them disruptive to the normal order of things, but Tara’s teen-age kids, Marshall and Kate (Keir Gilchrist and Brie Larson), barely bat an eye at their doings. The first one we meet is T, a sluttish, smart-mouthed fifteen-year-old. She’s Kate’s favorite, and is, like her, dismissive of Tara’s mothering. Kate enjoys T’s wildness; she herself has a flatter, Junoesque style, a compulsive epigrammatic disorder. Walking into the house after school, she calls out, “Yo. Is anybody home? Marshall? Estonian cleaning lady? Mommy?” Tara’s husband, Max (John Corbett), a member of that strange breed of TV husband that exhibits infinite patience, essentially has to juggle four wives, only one of whom he’s allowed to have sex with, because even though the alters share the house and his bed, and are in his wife’s body, none of them are his wife. Toward the end of the first episode, we meet - stand back - Buck, a loud, beer-drinking, profane, homophobic, trucker-cap-wearing troublemaker, who calls Marshall “Marsha” and gets into fistfights. Buck isn’t a lesbian; Buck is a man - he accounts for his missing penis by claiming that it was shot off in Vietnam. Then there’s Alice, who is right out of “Desperate Housewives,” a bustling, repressed homemaker, in a prim flowered dress and a starched apron. She brings order to the household and is a personified rebuke to Tara. Marshall and Alice have a bond; he finds her reassuring, especially after she cuts a punitive teacher of his down to size.

All three non-Taras seem to have a place in the family, but Tara herself doesn’t altogether know where she belongs. She genuinely can’t collect herself, though the stresses in her life that trigger the shifts to T, or Alice, or Buck, are not uncommon ones: her daughter starts having sex; Marshall is all gummed up with adolescent impulses that he doesn’t understand; and her love life isn’t what it used to be. There’s a rationale for each alter, but I don’t really know what the show as a whole is up to - whether each of Tara’s alters is meant to be seen as a missing part of her, or whether the show is a tableau vivant illustrating that it is the lot of all human beings to have their needs unmet, and that even united states are imperfect unions. Or perhaps “Tara” just is what it is: a story about a woman with D.I.D., period. The three alters are broad stereotypes, but Collette makes the moments of transition surprisingly touching, and sometimes subtly comic. Her ability to transform herself extends even to her physique: when she’s Tara, her head seems delicate, wedge-shaped; when she’s Buck, it’s a blocky oblong. Collette is impressively convincing, even though I’m not entirely sure what I’m being convinced of.