‘Charmed’ Adds Bewitching Twist

As TV plot devices go, the Evil Twin spin has shown remarkable staying power. Sometimes it’s a perk thrown to a disgruntled star who complains of feeling stifled. Other times it surfaces as a sweeps gimmick to kick-start ratings. It can also be a sign that the writing staff has simply hit the wall.

In tonight’s episode of “Charmed” (9 p.m., WB), series newcomer Rose McGowan does double duty with a couple of things in mind.

First, for viewers still mourning the departure of Shannen Doherty after three seasons, it gives McGowan bonus screen time and thus a chance to win over fans. Second, the plot of “A Knight to Remember,” in which the three witch sisters must go back in time to thwart McGowan’s evil otherness, helps bond the new trio in a manner that bodes well for the rest of the season.

Although one can’t help thinking back occasionally to the goofy Samantha-Serena matchup from “Bewitched,” tonight’s fairy-tale foray keeps things rolling on its own terms. Alyssa Milano as Phoebe and Holly Marie Combs as Piper have some amusing moments coming to grips with the new challenges that McGowan’s defiantly independent Paige character will be throwing into the mix.

Spellbinding stuff? Hardly. But it’s wickedly good fun nonetheless.