Robin Williams has proven himself to be equally expert in outrageous comedy characters or heartfelt dramatic ones. His latest film, The Night Listener, presents a sober Robin Williams playing a radio call-in host who befriends a dying boy in a phone relationship. When he becomes suspicious of the boy’s mother, he calls into question the very existence of the boy.

Getting serious is almost literally a flip of a switch for Williams. “I think that it's a choice,” he said. “There is a conscious choices. So, yeah, I can turn it off or on according to need or according to inspiration. If someone says something that seems like a nice opportunity I will go that way. I will attempt to find the comedy in a Spanish maid. So then we have moments like that and then you have moments where you realize it's okay and you can talk straight if you want.”

The Night Listener is based on an Armistead Maupin novel which he wrote after a real life experience. He dealt with a dying boy whose mother sounded suspiciously identical on the phone. The woman would never let him meet the son, but continued the relationship by phone. Getting familiar with the true story left Williams torn about the woman’s actions.

“I do [sympathize] and I don't because you also have kind of this compassion and say that there is something motivating that aside from the fact that she can. There is something disturbing her. If you've tracked her history like Armistead has, she went on to marry some man and that turned out to be a car wreck and then the fact that she contacted us, there is that weird kind of stalker mentality combined with the ability, she does have that ability, she convinced these people and she used it. You have to say wow to that. What did she do with it? She scammed people. She had them going and there's a certain amount of skill in that as with all great sociopaths who do that.”

After years without contact, Maupin believed that an anonymous letter sent to actress Toni Collette during filming was from his former contact. “I only know that it was kind of like, 'I hope you do this part well because it'd be great if you did it great.' It was well written and much more articulate than that. She wasn't on medication. But it was like Armistead noticed where it came from, I think, and plus the handwriting I think that he recognized. I mean, I think that after six years that he started to know the handwriting, and I think it was disturbing, but it was also like they thought that it would happen at some point.”

That alone was all the research Williams needed. “At a certain point you don't want to know too much because it'll creep you out and you won't be able to work that well. I mean, she exists and there are other people who have done it obviously. There's J.T. Leroy and other scams that have been perpetuated for a while. Sometimes it's against celebrities and other times it's against regular people. There was a thing in the paper the other day about a guy who scammed seventy thousand dollars from his friends by claiming that he had pancreatic cancer. What she did here is Munchausen's by ventriloquism – create a persona. People engage in that and think, 'Oh, this child.' People have a desire to help. It's the child factor or the puppy factor.”

It happens on a bigger scale too. “Look at the woman in Florida with the issue of euthanasia. That became a national political issue about whether she was dead or alive. Doctor's were saying, 'I know she's alive.' Then they perform autopsy and go, 'There was nothing left. There was no brain activity.' Basically doing the autopsy you find that out and they had played off of that and used, or they will use an incident of someone in desperate need or in pain and focus on that and a politician will be like, 'Don't you understand?'”

Perhaps The Night Listener is a warning to be wary of compassion. “You found that out after 9/11. There were all those people saying that they were there, a lot of people scamming. Any time there is money or some sympathy to be gained you will find people working the edge. Katrina. Billions of dollars. Then there are other people who have genuinely been screwed. Because the guilt was so huge after Katrina they just poured money at it and didn't bother to do the normal checks and meanwhile there are other people living in their houses with black mold or that they have ten thousand trailers in Alabama that aren't being used. Still, there's the Ninth Ward and a lot of those places that are abandoned or don't have electricity. It's like Baghdad. You can hear people in Baghdad going, 'I have more power than you do.' 'Goddamn. That doesn't seem right. I have better music though.'”

Luckily, Williams has been able to give without getting scammed. “I've helped a lot of Make A Wish kids, but I've never one call from the Bahamas going, 'I'm thirty. Thanks for the money for the dialysis machine. I'm riding it.' I've never been duped like that, but I have met other people who have been. There was also a woman going around here who was with a lot of comics, a coincidence, who claimed that she had a son who was severely handicapped or suffering from something and engaged them I think for money and for companionship. They were going with it and had never met the kid, or maybe at one point she did bring the kid, but it turned out later that it wasn't even her kid. She borrowed some kid and so it is out there. As we've seen with J.T. Leroy and stuff there are books where people are like, 'Oh, this book is so devastatingly sad and real.' And it turns out that it's a couple in San Francisco.' And Oprah is going, 'Don't you ever offend the queen of show business.'”

Being a master impressionist, Williams has perpetrated a few scams of his own, but only for fun. “I've called up as different people so sometimes I'll call people and do that or I'll answer the phone if it's someone that I don't want to talk to with a Chinese accent. In San Francisco if you answer the phone with a Chinese accent solicitors go, 'Sorry to bother you. Sorry to bother you. ' I think that I can do Jack for some people. On the phone it's fun if you call girls and go, 'Hey, is mommy home?' That always gets you an interesting response. I think that works well. I mean, there are accents and things that I can do sometimes if necessary to work off of people which is fun.”

The Night Listener opens Friday