These days, a lot of TV actresses are taking on dual roles: The Vampire Diaries' Nina Dobrev (Elena/Katherine), Ringer's Sarah Michelle Gellar (Bridget/Siobhan) and The Lying Game's Alexandra Chando (Emma/Sutton). But back in 1963, Patty Duke was all on her own as identical cousins Patty and Cathy Lane on The Patty Duke Show. "We didn't have digital anything," recalls Duke, 64. "We'd [shoot] the Patty side first, then everyone would stand in place while I sneaked off and came back dressed as Cathy. In postproduction, they would actually split the celluloid."

Tonight Duke is returning to TV for a guest appearance on Hawaii Five-0. It's a role she couldn't turn down. "I play a woman in the second stage of Alzheimer's whose son was involved in a nefarious deal with gold coins in the ocean," says Duke, who took home the best supporting actress Oscar for The Miracle Worker in 1962. "McGarrett [Alex O'Loughlin] and Lori [Lauren German] come to inform my character that her son is dead and find that I'm living 20 or 30 years in the past. In her head, [her] son is still a boy coming home from school any minute for a sandwich."

Duke knows all too well what it's like coping with mental illness, having battled bipolar disorder for decades. Grateful that it's been three years since she suffered her last episode of severe panic attacks and irritability, she will continue taking her meds for the rest of her life. "I've been on this medication for 30 years and just want to throttle the people I meet who tell me, 'I don't need it,'" she says. "They have that right, but not the right to impose all the results that come with that on their friends and family."

The proud mom of actors Sean Astin (The Lord of the Rings) and Mackenzie Astin (The Facts of Life), Duke admits having leaned heavily on her former TV dad, William Schallert, now 89. "He's just amazing," says Duke, whose own father left the family when she was 6. "He has been 90 percent the dad I never had. No matter what craziness I was [going through], he was always there for me."

Still, she admits there were times the two butted heads as active members of the Screen Actors Guild. "I would get so pissed at him when he challenged me," she remembers with a laugh. Yet it was only smiles when the longtime pals reteamed with the rest of their sitcom cast for a 1999 TV-movie reunion. Actress Jean Byron, who played mother Natalie Lane, passed away in 2006 at age 80.

Having finally tired of the fast pace of Los Angeles, Duke now lives in Idaho with her husband of 25 years, retired firefighter Michael Pearce. Says Duke of L.A.: "I simply would not have another stranger give me the finger."

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