HEATHER LOCKLEAR MELROSE PLACE Prime-time crisis: In 1992, jiggle king Aaron Spelling tries a sincere twentysomething version of his bubblegum hit Beverly Hills 90210. The end product proves less palatable than fat-free dust. Heather to the rescue a year later as: Amanda Woodward, spectacularly insincere ad exec, lewd landlord, and tireless campaigner for that trashy bleached-blonde-with-dark-roots look. Special qualifications: Is a real Renaissance woman. In the mid-'80s, Heather proved she could wear crotch-length skirts and still bust balls with her legendary double shift as a regular on both T.J. Hooker and Dynasty. Rock on, Newt!: Heather digs both heavy-metal guys and the flat tax - she's a registered Republican! Ratings result: Doubles viewership among 21- to 29-year-olds; transforms the show from nonviolent bore to official shlockfest of the'90s.

LAURA LEIGHTON BEVERLY HILLS 90210 Prime-time crisis:Vixen Tiffani-Amber Thiessen deserts the ZIP code just as 90210 goes head to head with rival Dawson's Creek. Who will fill the good-natured-slut void? Laura to the rescue this fall as: Actress/tramp Sophie Burns. Special qualifications: Knows the territory. As Sydney, Melrose Place's good-natured slut (1993-97), found work as a hooker, a medical secretary, and a Heidi Fleiss-style madam before getting squashed by a truck on her wedding day. Screen-saver handicap: Grew up without a TV; was unable to study the impact of new cast member "Oliver" on The Brady Bunch's final season. Ratings result: Come on...no one can save this Rodeo Drive relic.

ALYSSA MILANO CHARMED Prime-time crisis: Last summer, the WB brews up a new sorceress drama about three Sabrinas and their curvaceous cauldrons. The haunting question: Will the show's star, real-life witch Shannen Doherty, scare viewers away? Alyssa to the rescue this fall as: New, extra-sexy witch Phoebe Halliwell, replacing less fetching cast member Lori Rom at the last minute. And who's the boss of the coven now? Special qualifications: Is an experienced hypnotist. Alyssa worked pubescent magic on '80s sitcom Who's the Boss? and bewitched as a boyfriend stealer on Melrose Place in 1997. Currently, billions of Alyssa Web sites zombify the world's youth. Un-witchy hitch: Offscreen, Alyssa (like so many otherwise sane women) has a thing for angels. Ratings result: The series debut breaks network records and sends ratings soaring 147 percent above those of comparable shows last year. Shannen who?

Laura Leighton could have helped 90210's ratings if her character were more like Sydney. But Sophie was just awful. And the way she was written off - it was so contrived.