Harry Potter and the Prisoner of Azkaban is the third film adaptation of J.K. Rowling's celebrated novel series, in which Harry and his friends Ron and Hermione, now teenagers, return for their third year at Hogwarts.

This time, they are forced to face their darkest fears as they confront an escaped prisoner who poses a great threat to Harry.

A dangerous and enigmatic wizard, Sirius Black (Gary Oldman), has escaped Azkaban prison and is believed to be searching for Harry. Legend has it that Black was responsible for leading Lord Voldemort to Harry's parents and ultimately to their subsequent deaths; it is also believed that he is determined to kill Harry too.

To make matters worse, Hogwarts is playing host to the Dementors, the terrifying Azkaban guards who are stationed at the school to protect the students from Black. The Dementors suck the souls from their victims and, unfortunately for Harry, they seem to have more of an effect on him than the rest of his classmates.

Meanwhile, Harry's time at Hogwarts is filled with eerie encounters with Divination Professor Sybill Trelawney (Emma Thompson) and the omen of death known as the Grim; and breathtaking adventures, including clandestine visits to the wizarding village of Hogsmeade, deciphering secrets hidden in the enchanted Marauder's Map, and a terrifying trip to the Shrieking Shack.

Along the way, Harry will try to make sense of Hermione's (Emma Watson) puzzling appearances and disappearances, with the help of Ron (Rupert Grint) and the giant Hagrid (Robbie Coltrane), who has taken on a new position at Hogwarts as the Care of Magical Creatures teacher.

A confrontation between Harry and the menacing Sirius Black seems inevitablebut what exactly is Professor Lupin's relationship with Black? What is the dark secret that Professor Snape (Alan Rickman) is so eager to reveal? And just why is Ron's pet rat Scabbers so frantic to escape his grasp?

Harry will need all of the courage, magic and support he can muster to answer these questions and uncover the truth behind Sirius Black and his ties to the gifted young wizard's mysterious past.

"Even though on the surface this is a story about magic and magical creatures, it was the issues explored in it that were so interesting to me, and so relevant today," says the acclaimed writer-director Alfonso Cuarn.

"Issues about growing up, identity, relationships with friends, the lack of parental guidance and the search within. There are also issues about social class, injustice, racism things that affect all of us around the world."

Author J.K. Rowling gave Cuarn her full support as he endeavoured to bring her exciting yet contemplative third novel to the screen.

"Jo Rowling asked me not to be too literal with my interpretation, but to be faithful to the spirit of the books," relates the director.

Daniel Radcliffe, who reprises his role as Harry, tapped into what he describes as "the teenage angst" in Rowling's novel for his portrayal of thirteen year-old Harry Potter.

As he sees it, "Harry is a very angry young man. He's not afraid to talk back to the Dursleys, nor to confront his own identity, although I think as with any other teenager his anger is balanced with a kind of social awkwardness."

As Harry confronts startling revelations about his past, Hermione also experiences a coming of age of her own.

"In the first two films, Hermione is the sensible one, always knowing what to do," says Emma Watson of her precocious character, whose Muggle heritage is a point of contention with Slytherin nemesis Draco Malfoy.

"In the third story, Hermione decides she's not going to take it anymore, not from Malfoy or anyone else. She ends up punching Malfoy and storming out of a class. She's more girl power,' more outrageous, and of course more fun to play."

Harry Potter and the Prisoner of Azkaban also introduces several mysterious new characters. To play escaped convict Sirius Black, the filmmakers turned to versatile actor Gary Oldman.

"The whole story is based around Sirius Black, the only prisoner to ever escape Azkaban prison, who everyone believes is trying to kill Harry," notes Alfonso Cuarn. "But Black is a character with many layers. It was an extremely challenging role to play, even for an actor of Gary's calibre."

Professor Remus Lupin is played by David Thewlis. "Lupin is very avuncular and likeable, but he also has this dark secret," says Thewlis. "He's one of the last surviving links between Harry and his parents, along with Sirius Black and Professor Snape. So Lupin is a great comfort to Harry, which was part of the appeal of the role. Many of the scenes I have are with Daniel no special effects, just conversation which was very rewarding for both of us."

Michael Gambon joins the cast as Hogwarts' esteemed Headmaster Albus Dumbledore, a role played by the late Richard Harris in the previous two Harry Potter films.

"People often ask me what it's like to be taking over from Richard Harris and I liken it to King Lear," Gambon relates. "So many actors have played Lear, and none of us worry about what the previous actor has done; you just take the part and make it your own."