There, at last, Dahl-mad DeVito was able to look at the original manuscript of Matilda, written with Dahl's special Ticonderoga pencils on the American yellow legal pads he used for all his work.
"I feel very close to Roald Dahl, to his sense of humour, and the characters he created. It was very moving to walk into that little shed and see where all those wonderful stories were written," says DeVito, back in his suite at the Dorchester Hotel. He enthuses about the Dahl shrine, seeing everything preserved just as it was when the world's best-selling children's author died in 1990. "That old plastic curtain with the holes in it, the primitive little heater on the wall, the grisly hip bone he kept after his hip replacement, the pictures of his children and the nicotine-coloured walls..."
He couldn't wait to show his children Lucy, Gracie and Jacob. They will be joining him for Christmas in Britain after they break up from school, together with his wife and Matilda co-star Rhea Perlman. She plays Matilda's materialistic, unmaternal mother, Zinnia Wormwood - the perfect mate to DeVito's philistine used-car salesman, Harry Wormwood.
It was 13-year-old Lucy who first sparked off her father's love of Dahl. "She brought the book of Matilda home about three years ago and said, `Mummy, Daddy, it's my favourite book in the world and we must read it together' - we have this habit of reading out loud together." (Roald Dahl would have approved.)
"When I read it with the kids, I saw how empowering it was, and I said to Rhea, `This would make a great movie and there are two great parts for us. Wouldn't it be fun to play the parents from hell and then have your real kids say how great you are by comparison?"
The macabre mirth of Dahl has a powerful appeal for DeVito, who made his name as a director with black comedies such as Throw Momma from the Train and The War of the Roses. Like Dahl, DeVito believes passionately in the power of reading and, appropriately, Matilda is a story of a little girl who loves to read and is prevented from entering the magical world of books by her parents, who live in front of the TV set when they're not painting their nails or doing dodgy deals on used cars. Matilda (Mara Wilson) is sent to a terrible school with a terrifying headmistress (Pam Ferris as you've never seen her) and develops telekinetic powers and gets her own back, with the help of an empowering teacher (Embeth Davidtz).
"Dahl will lead a child's mind out on to a windy limb and then suddenly he'll place a ladder underneath and the child will be able to get safely to the ground," DeVito says. "In Matilda I tried to bring them to the edge and then give them that escape hatch. It's really important to elicit those responses. People said, `You're not really going to throw a kid over a fence, are you?' But I got Pam [Ferris] together with a real Olympic hammer-thrower and it really worked!"
DeVito acts out much of what he says, fidgeting and half standing in his chair, or leaping up from it, to make a point.
He judged how far to go in making "that sweet Pam Ferris" terrifying as Miss Trunchbull by monitoring the reactions of his own children. "I also held special screenings for audiences of up to 150 children," he reveals.
"I usually hide somewhere - behind a curtain, or a two-way mirror - and watch their heads, see when they're on the edge of their seats and when they're talking. You can learn a lot about cutting a film that way!"
He is delighted to think he has something of a child's perspective himself and understands it in his filming of Matilda (making Miss Trunchbull look even more enormous by letting the camera adopt a child's eye view). I do not ask whether this is in any way due to his diminutive size - size seems irrelevant in our meeting as his presence is so large it fills a room. His big brown eyes twinkle as he talks and his dark hair flies out animatedly from either side of his balding dome. He talks like an ordinary guy from "Joisey" (as they say in his native New Jersey) and not like a film star.
Spending years struggling as a character actor in New York, where he met Brooklyn-born Perlman in 1971, may have helped him to retain a refreshingly realistic mindset. He only uprooted to LA after the success of One Flew over the Cuckoo's Nest in 1975.
Perlman has acted for her husband before but never with him, and really revelled in her role as the brazen, blonde, bottom-wiggling Mrs Wormwood, says DeVito. "She loved going shopping for clothes for the part. There wasn't a night I came home that I didn't get glitter on me!"
DeVito admits he couldn't resist the dramatic opportunity of narrating, directing and starring in Matilda. His voice-over was originally intended for the cutting-room floor. "And I had some friends read for the narrator - good actors, not chopped liver," he winks, "but it always seemed better the other way." He is confident that children can distinguish between DeVito the friendly, omniscient narrator, and DeVito the horrible Harry Wormwood - and so is Liccy, Dahl's widow, who insisted the narrator had to be a man's voice, and that Danny's was the best if it couldn't be Roald's.
Liccy maintains that in many ways, however incredible it may seem, DeVito reminds her of her late husband. "He'll say things that are so like Roald!" she cryptically comments, declining to elucidate.
DeVito made the first of hundreds of calls to Liccy Dahl three years ago to ask if he could buy the film rights.
"She said that someone was already writing a script on spec but I kept on calling and calling." He grins, clamping a large cigar between the teeth that are as difficult to prise open as a tenacious terrier's, he admits, once he gets them into something.
Persistence paid off, because three days before the script was due to go in the open market, Liccy "tipped a wink" to DeVito that it would be up for sale. "But in Hollywood," he shrugs, "money talks, and a lot of the time the right person doesn't get the film. It just goes to the highest bidder."
So Matilda went to Universal. "But the ace I had in the hole was that Liccy Dahl had director approval. I was going to direct it for the Roald Dahl Foundation but there were all kinds of problems and then the studio decided it didn't want to make it after all, so we bought them out."
Not for a pittance, either, he makes clear. Although DeVito is as coy about sums as he is about adapting the work of a dead writer whose intentions are more assertively protected by his widow and the foundation she set up in his memory than they were by the author himself.
"Thank God that Liccy is taking care of Roald's memory and material," DeVito says fervently. "That needs to be done. But I never felt I didn't have a free hand. A screenplay is only a blueprint, and a film has to be a collaborative effort, so the faxes were flying back and forth with suggestions and comments, but no one ever said `This is the way it has to be'."
`Matilda' opens tomorrow. See Ryan Gilbey's review, page 6