Mel Gibson is ringing the changes on a new, all-singing, all-dancing, all-American The Singing Detective. Time Out headed for Hollywood to get the scoop from star Robert Downey Jr., director Keith Gordon, and a bald old coot in glasses

Robert Downey Jr. is seeing a shrink. He looks like shit. His skin is pocked. Scabbed. Blistered. His coloring is red-raw and angry - it's like his whole body is festering and flaring. You want to lean in and adjust the chroma - except you can't because this isn't TV, it's happening right in front of your eyes. He's in a wheelchair, his back clenched, his neck, his legs, his hands clenched like mitts in front of his throut. Behind him, the shrink is a bald, bespectacled old coot. Oddly, he seems to be improvising some sort of soft-shoe shuffle.

"There are puzzles, mysteries... things that bewilder us," the old coot counsels. "Accept it. Yes?" Downey is unimpressed. "Accept the sky. Accept the birds. Accept birdshit," he spits. "The way you walk behind me... Are you pretending to be an oddball, or are you really nuts?"

That's the seven million dollar question all right: underneath Doctor Gibbon's baldcap, his rubbery old face and ultra-thick eyeglasses lies one of Hollywood's most successful players, an Oscar-winning director, a producer wealthy enough to back more than a dozen movies a year, and a good old fashioned movie star. Not to mention a staunch Catholic father of seven. What's a guy like Mel Gibson doing with a bilious post-modern psycho-noir-musical comedy like The Singing Detective on his slate? And why would he cast Robert Downey Jr. in the role Michael Gambon stamped with such patent authority?

Dr Gibbon has a question too. "Do you plan to get better, Mr Dark?" - meaning his impatient patient, Downey. "Chronic illness is a good shelter - a cave in the rocks into which a wounded spirit can safely crawl..."

Ouch, but that has to hurt! Consider: here we have "one of the most gifted actors of his generation™," whose fame now resides in drug busts and repeat parole violations - an actor whose career was widely pronounced over after he blew his big comeback gig on Ally McBeal when he was arrested in possession of cocaine in April 2000. Here he is, a year later, out of rehab, and Mel Gibson on his porch with a screenplay in his hand and a twinkle in his eye. "In some ways this whole movie is an act of generosity on Mel's part, a gift to a friend," director Keith Gordon suggests when the crew break for dinner. Gibson and Downey are old pals from Air America, a disappointing buddy movie back in 1990. "Mel wanted to remind everybody what Robert could do."

Gordon - a teen star himself in Christine, Dressed To Kill, and Back To School (with one Robert Downey Jr.) - had been tracking The Singing Detective ever since Dennis Potter turned it into a movie script ten years ago, pruning five hours of material from seven, transplanting it to America, and updating the detective story to 1950s film noir. "Potter did a brilliant job, but it was always with some huge star and huge director attached as a $50 million movie. I couldn't get near it," he says. "But in the end, Hollywood was never going to make this as a $50 million movie."

Gibson's company, Icon, acquired the rights three years ago. Knowing his interest, they approached Gordon nine weeks before shooting after another director dropped out. "Mel is the only reason this is happening - because he's brave and cool enough. He thinks 'I'm a successful guy, let's take a risk and do something special.'" Hence his forthcoming directorial project on the life of Christ, which is said to be entirely in Aramaic, and which Icon plans to release without subtitles. (Then of course, there will be Mad Max 4.)

On set, Gordon lets this four-page scene play out in long, unbroken takes. It's a pleasure to hear the rhythm of Potter's dialogue as doctor and patient fence. Occasionally Downey throws in something new - "Dr Dolittle" becomes "Dr Do-Less" in one take, "Dr Do-Nothing" in the next. Gibbon taunts Dan Dark out of his cave for a moment, only for him to scuttle back when he suspects the doc might have been talking to "a certain high-class whore of my former acquaintance" (his wife, played in the movie by Robin Wright Penn). It's typical Potter: an intense, barbed trawl through murky self-revulsion as his stricken writer alter-ego tries to put sick body and quick, sick mind back together again.

Between takes, Gibson fools around with anyone who crosses his path. Downey might join in the repartee, but remains immobile, staring down the lens of a camera just inches in front of his face. "They're quite similar people," Keith Gordon observes. "They're the kind of people if you met them at a party they would keep you laughing for two hours. They're wacky and funny and bold, then when they get quiet, you see there's a whole other layer they're not going to show everybody: sensitive, complicated, quiet, sad. They prefer to stay on the surface, I think." He gives Downey a clean bill. "People assume that people who struggle with drugs are wigged-out monsters, but Robert did 35 movies and TV series and he was always fine, a consummate professional. On Back To School he was a blast. He was good at hiding it, which is why it went on as long as it did. Now he's completely clean, and maybe he's a bit more serious, but he was 23 then and he's in his late thirties now. You grow up a lot in that time. I think it's interesting that Dan Dark is having to deal with his past, to work through it in order to move forward, because that's where Robert is in his life."

The two stars elect to be interviewed together. They're both in costume and hidden behind layers of glue and latex. They kid around. Downey even makes a point of scratching his flaky skin over my microphone: it sounds like Niagra on my tape. "If you're gonna deal with Icon, you've got to be prepared to work for... scale," he joshes, with a deliberate wince. "I look like Ron Howard's dad," offers Gibson. "Every shrink I've ever met has been a weird cat. I think they're crazy."

Does Downey prefer playing the invalid writer, or his detective hero? "Just watching Mr Gambon made me uncomfortable," he admits. "But I was more scared of the singing detective stuff. It's been a long time since I did any musical theatre, and even as the detective, I didn't know how cool I could be - whereas Mel just turns it on." "I knew he could do it," Gibson vows. "Especially the suave part. No doubts about it, Gambon was tremendous. He made himself handsome just through attitude - that's a great actor. But so is Robert."

How willing was Downey to explore his own darkness? He shakes his head. "Not as willing as I thought! Sometimes things are close to home. It's obvious this guy's in excruciating pain and it's obvious he's furious, so I think I've trusted myself to be a bit more technical on this than emotional, to be objective about the performance. But it's easy to say that, not so easy to trust it. But you know, add rubber (make-up), you're pissed already - so that helps."

He's grateful for Gibson's support. "It was less than an ideal time to be saying, 'Let's put Downey at the front of the list and ride a whole bunch of dough on the guy.' It's been a while, actually. And it never entered his mind..." He breaks off. "His faith in me has really meant a lot." He seems genuinely moved, but Gibson is having none of it: "I just want to work with people I like and he's one of them. Also, every two weeks I send him a Polaroid of my cock laying across a chopping block."

"I don't have much survivor's guilt, I'll tell you that," Downey insists. "There have been times, a lot of fucking years, where I've been showing up and kicking ass. I've paid my dues tenfold. So fuck 'em!" His defiance evaporates almost immediately. "I was tripping going into this, I must say. I was freaking it. Mel, God bless him, had to manage me a bit. But once we started, it's been great, probably the best experience..." He trails off into self-doubt again: "It has to be good, because of the original. It's a big deal." He means it too.

Back on the set, Keith Gordon comes over. "I love acting," he confides. "Hated being an actor. Two wildly different things. Being an actor is auditioning, unemployment all the time. It's very unhealthy. Acting is pretend and play and fun."

I hang around and watch them run through the scene again and again and again. Every time Gordon calls, "Cut," Robert Downey's scabby, pock-marked face breaks into an irresistible 1000-watt smile. It seems to me those smiles might be worth holding on to. Too bad they'll end up on the cutting room floor.