Some of the most popular characters in modern literature for young people return to the screen in the third film adapted from a best-selling novel by English author J.K. Rowling. in Harry Potter And The Prisoner Of Azkaban.

It is a new semester at Hogwart's School of Magic, and this third and darkest-yet Harry Potter screen adventure finds the young wizard in great peril.

Why would someone want to kill Harry Potter? Perhaps it's because Sirius Black was imprisoned for murdering Harry's parents; and perhaps it's because confronting him could bring young Harry closer to the father and mother he never knew.

Daniel Radcliffe is back as Harry with Emma Watson and Rupert Grint returning as his best friends Hermione Granger and Ron Weasley. The director of the first two films, Chris Columbus, takes the role of producer this time and turns the directing task over to Mexican-born filmmaker Alfonso Cuaron, who admits he did not know much about "Harry Potter."

"I had not read the books or seen the movies," he admits. "I obviously knew about Harry Potter, but for some reason I thought it was just a big, cheap franchise. I was not into it [and] thought it was something really silly."

But his opinion changed after he read the screenplays for the first two films as well as Prisoner Of Azkaban.

"I read the scripts and said 'I'd better read the books.' I read the books and said 'I'd better do this.' It is so awesome. It is so layered. I don't care if they are wizards; they have real human emotions and many levels of meaning. More than just an adventure, you can see it as a metaphor about racism and classism and power ... and also about friendship and loneliness," he says. "For me this is the story of one kid seeking his identity as a teenager. Together with that is the journey of this kid accepting his male energy ... the energy of his father inside him. What I mean by that is there is an energy identified with his father and that same energy resides inside himself."

Almost 15 now, Daniel Radcliffe says he can still identify with the issues his character is facing.

"Harry, being a teenager, feels the same feelings as every other teenager feelings of anger and loneliness but because of his past, I think he feels them more," explains Radcliffe. "That was kind of hard for me, but because I obviously am feeling the same things as him I took what I was feeling and exaggerated it. I would listen to music or anything to get me in the right state of mind ... and then hope for the best until I was in there, really."

Among all the cast members, Emma Watson is the acknowledged expert on the original books; and she predicts Potter fans will definitely be pleased by this adaptation.

"A lot was cut, but they did a great job of making sure that everything put in the film was really relevant to the plot," she says. "One of the things I think is really nice about this film is that it's really fast-moving and I think they did a really good job of getting everything that was important in there."

Veteran character actor Michael Gambon takes on the role of Hogwart's master Dumbledore, replacing the late Richard Harris who played the venerable professor in the first two films. Watson and Radcliffe agree the difficult transition works well.

"Obviously it's very hard to follow on for Richard Harris who a lot of people thought was the perfect Dumbledore; but [Michael Gambon] did a really great job because instead of trying to make himself look like Richard Harris or try and copy him, he did his own thing with it and put his own spin on it," Watson says.

"I think he's kind of a mischievous Dumbledore," adds Radcliffe.

As everyone keeps mentioning, this is the darkest Potter film yet: in part due to the nature of the original book and in part from the style of director Cuaron. However, Scottish-born Robbie Coltrane, who returns as groundskeeper Hagrid, is confident the kids can handle it.

"The truth of the matter is children can watch quite a lot of scary stuff, so long as they are close to an adult that they trust at the time. It seems to have a different effect on them," he says. "I must confess that I thought I wouldn't want my six-year-old daughter to see this one, because you just assume they would have nightmares and be scared; but I think their tolerance of scary stuff is so much higher than when we were kids. Well, we never saw any scary stuff, did we?"

Harry Potter And The Prisoner Of Azkaban brings back Alan Rickman as Professor Snape and introduces several new characters including David Thewlis as Professor Lupin, Emma Thompson plays Professor Trelawney and Gary Oldman is gleefully menacing as Sirius Black.