Robert Downey Jr. has always indulged his dark side - but lately he's started to see the light.

Robert Downey Jr. needs a boost. The actor arrives at a London restaurant for lunch at 2 p.m. with an internal battery that is decidedly flat. "The first thing I need is a cappuccino," he says before he even glances at the menu. He orders it (with skimmed milk and honey), but it takes a long time to arrive, and Downey - who borders on the hyperactive even at normal times - grows ever more fidgety. "Where's the coffee? Should we start? No, let's wait. I can't kick in until I get a cappuccino. You'll see. The words will really start to flow then." So he sits, jiggling his foot, brushing his newly long hair away from his face, playing with this little brown purse that is all he's carrying. Small talk about his wife, the actress Deborah Falconer Downey, and their 10-month-old son, Indio Falconer Downey, and his sort-of, but not strictly, vegetarian diet: "It's not really a diet; it's these rules I break occasionally. Every now and then I'll chow down on a Tramp burger." The cappuccino finally arrives, and Downey immediately orders another one - as well as an iced tea and a pack of cigarettes. Then he leans over his coffee cup with almost religious regard and takes his first sip. "Ahhhhhhhh. Now we can start."

Downey's desire for a caffeine kick-start is understandable given his recent schedule. He's in London for three months shooting the costume comedy/drama Restoration, in which he has the starring role over Meg Ryan, Sam Neill, Polly Walker, Hugh Grant and David Thewlis. Meanwhile he'll be seen in two upcoming films in the U.S.: Oliver Stone's Natural Born Killers, in which he plays an irksome television reporter documenting the deeds of killers Woody Harrelson and Juliette Lewis, and Norman Jewison's romantic comedy Only You, in which he's the sort of Tom Hanks goofy leading man opposite Marisa Tomei. He admits the two roles couldn't be more different, but predictability has never been one of his strong points, either in life or acting. Downey ad libs his way through everything. Once his spiel is cranked up there's almost no stopping him, as he veers headlong from one subject to the next, from an English to a Viennese accent. The variety of his talents, even in an interview, is what makes him so fascinating to watch on screen.

It was Downey's idea to do an accent for the Natural Born Killers television reporter, who starts by glorifying the murderous couple and ends up being taken hostage by them. He was going to do a British accent but Stone nixed the idea since Downey had just done one in Chaplin. "So one day I came to the set and started talking Australian," Downey relates as he walks across Tower Bridge after lunch. Suddenly he begins to reenact entire scenes in a broad Australian accent not unlike Robin Leach's. The role in Natural Born Killers is the type of crazed, on-the-edge-yet-likable part that Downey has done throughout his career.

Now the challenge is to soften the edge. It's the romantic lead in Only You that could finally make him a big (i.e., box office) star. "I don't know why my films haven't been more successful," he blurts out without prompting. He has complete confidence Jewison has treated him well. Downey says he took the part in Only You after Jewison said those two trigger words: 'Cary' and 'Grant.' When it's pointed out there's another pretender to that title - Englishman Hugh Grant - Downey quickly reverses himself. "Perhaps we should say 'Gregory' and 'Peck.' Or 'Gregory' and 'Grant.'" "Robert has always had charm, but he never used it in the way other actors have used their charm," says Jewison. "All of his roles demand so much and he is always in character and interesting to watch, but he's never been allowed to play a kind of starring role - with style and charm - until this film. He's like Tony Curtis: charming with great comedic timing."

Downey, the son of offbeat screen director Robert Downey Sr., has been acting since he was five when he made his debut as a dog in his father's film Pound. He later fell in with the Brat Pack by starring in that premature homage to the X-generation, Less Than Zero, but even his eerily accurate starring role in Chaplin couldn't send his career into the Hollywood stratosphere. The combustible combination of Downey's hyperactive creativity, mixed with a predilection for substance abuse, almost led to a burnout a couple of years ago. "When I'm giving somewhere up around 96 percent, I begin to wonder if I'm taking it all too seriously. Basically I've always acted like I was doing it for longer than I was," Downey says. "I was thinking about that today: where did I get the confidence from? I just think it was part of me. I think there are certain parts of our life that are shaped by our environment and then another part that is the toolbox given to us before we get here. Acting was in my box."

His current appreciation of his career is in direct opposition to how he handled the earlier years. Downey spent the Eighties on a drug-and-alcohol binge that ended only when he checked into a rehabilitation clinic five years ago. He describes his entire experience of the Me Decade as "trying to wade through a room packed with styrofoam packing balls." "I think five or 10 years ago we were all very daring in a not very useful way. We'd suddenly blurt out, 'Let's all go four-wheeling!' We were all on some kind of quest. Now we recognize that we can still be wild if we want to be, but then we have to recuperate. It's easy to be lost in Chablis heaven, but that's not a very efficient use of our time. So no more debauched double-vision quests are allowed."

And what drove him on that quest? "Some people tune in and some tune out. For me, it was always about wanting intimacy and about trying to be sllooooow. But I'd go into overdrive straight from third gear. Now I force myself to downshift or go into neutral. I run myself a bath and sit in it until the temperature changes." He pauses, then brightens as he begins a self-critique of the interview. "How's it going so far? I think it's going well, don't you? I think we have some good quotes, some good jokes. I think it will work out really well."

What's undoubtedly helped calm him down is his marriage to Falconer. The two met after Sarah Jessica Parker ended her seven-year relationship with Downey in 1992. Downey says they're still friends and write letters "or call each other, tell all our secrets in five minutes and then hang up without saying goodbye." But almost every part of his conversation circles back to his wife, who simply telephoned him one day to introduce herself. "That's what makes Only You so realistic," Downey says. "If I had let the answering machine get her call, we might never have met. There are hundreds of things that had to happen before we did. But the flip side of that is that no matter what, thousands of things happen, if you are meant to be with that person, you will be. We are still trying to figure out that exact science of looove. But there's also some chaos in operation there."

Downey is now decidedly the family man. The couple and Indio live just north of Los Angeles and are trying to sell Downey's old house in the Hollywood Hills, which used to belong to Charlie Chaplin. "If we don't sell it soon, I'll be doing commercials in Japan for money," he jokes. He now spends most of his time at home either writing music or working on a screenplay that takes a surreal look at the Eighties. He hopes to direct it soon, although he won't act in it. "Everything these days gets cleared through Debbie," Downey says. "Anything except a drive to the health-food store for soy milk and tofu goes up for her judgment. I no longer feel the need to be constantly doing something all the time."

Her judgment even extends to his clothes. Downey has long been one of Hollywood's sharpest dressers, which he said was a reaction to years of wearing hand-me-downs and red rubber galoshes as a child. He dove deeply into designer wear "as soon as my per diem became bigger than my weekly salary. But my style used to be much wilder in the Eighties. Now I'm totally into comfort, so it's big pants and easy T-shirts." When he does have to dress up, his favorite designers these days are Dries Van Noten and Matsuda, "the god of the century." He also liked the Giorgio Armani suits in Only You, one of his first roles where he got to be so stylish. He complains the costumes in Restoration are at the other end of the spectrum. Downey and the rest of the cast spend most of their time in shoulder-length wigs, pantaloons and frock coats. The film recounts the 17th-century story of adventurer Robert Merivel, who is invited by King Charles II (Sam Neill} to become his royal physician, but then gets into all kinds of trouble with Polly Walker and Meg Ryan. Director Michael Hoffman has been trying to do Restoration for the last three years but only managed to get the financing together earlier this year. Downey is so enthusiastic about the project he almost jumps out of his seat talking about it and raves about working with Neill and Thewlis. "Most of the scripts I get end up in the corner all scrunched up after 30 pages, and I'm insulted they even sent it to me. This one feels like we were all meant to be doing this particular film at this particular time. We almost don't want it to end."

End it will, and Downey doesn't know what's next. He'll go home to LA., relax with his wife and son and work on his screenplay and music. After years of searching, he seems to have found his slot. "Hoffman says, 'Know your purpose, accept your feelings and do what has to be done.' There is still a lot of kidding yourself, but his idea works. I guess I've just wokened up a lot." Downey will be 30 next year, by which time he will have been acting for a quarter of a century. As he lounges in the back of a taxi taking him to a photo shoot, he claims the passage of time doesn't bother him. "No one can say my career's flown by or it's all been a great time, but I'm looking forward to turning 30," he says as he stares out the window as the streets of London pass by. "I think it will be a blast. It's partially because it's a way of saying, 'I made it.' And 30 is the age that justifies everything you've been doing up to now. Suddenly that's when it all begins to make sense."