To film critic Billie, there are three stages of womanhood: Meg Ryan in 'Sleepless in Seattle,' Meg Ryan in 'You've Got Mail' and Meg Ryan in the grocery store saying, 'No, really, I'm Meg Ryan.'

Billie lives in a San Francisco, where she's a full-time film critic who has gotten stuck somewhere between You've Got Mail and the grocery store. She's heading toward 40 and recently dumped her rich boss when he refused to propose, so now Billie is sowing her oats -- leading to a two-night stand with Zack, who is considerably younger than herself -- that leaves her pregnant.

What's a 37-year-old film critic to do? The answer makes up the contrived, fantasy plot behind Accidentally on Purpose, a fast-moving, occasionally amusing series that premieres Monday at 8:30 p.m. EDT/PDT on CBS, the greatest asset of which is that it gives sunshiny Jenna Elfman a new platform for her Lucille Ball-inspired graceful mugging.

Accidentally doesn't wait around to get moving; by the end of the first 22 minutes, Billie is pregnant and Zack has moved in. But they're not in a relationship, she insists -- they have to save something for Episode 2. By then, audience heads should be spinning (and mouths watering): Zack is the nicest, if most lightweight, guy on the planet, cooks a mean ravioli and smells like a Skittle, Billie says. I tasted the rainbow.

But Elfman perseveres. All wide-eyes, splayed fingers and sudden movement, she still is the perkiest, most likable thing in the room. But she needs a cast equal to her talents, and instead she's saddled with a leading man in the wooden Jon Foster, who always seems to be looking over her shoulder. That is a fatal flaw.

In the end, what surfaces is more the Purpose than the Accidentally: This is an utterly predictable comedy (what, you don't think Zack and Billie will fall in love in Season 2, right after he starts dating another chick and Billie has an epiphany?) that's got a few fun lines.