LONDON (Reuters) - Nicolas Cage is working hard because he has to, but his latest turn as a mediaeval knight in "Season of the Witch" is about more than just paying the bills -- it is a welcome throwback to his childhood.

The supernatural thriller set in plague-stricken 14th century Europe opens in British and U.S. theatres on Friday, and Cage fans will see the "Leaving Las Vegas" star in the unfamiliar surroundings of a period drama.

"For some reason I kind of got swept up in a certain modern and contemporary style of acting and drama, like 'Bad Lieutenant'," the 46-year-old Oscar winner told Reuters in a recent interview to discuss the film.

Season of the Witch follows "Bad Lieutenant: Port of Call New Orleans," Werner Herzog's cop drama in which Cage plays the kind of emotionally intense, borderline unhinged character for which he has won most acclaim.

"This (Season of the Witch) was my first chance to really go into the source, the childhood.

"When I was living in California ... my father built this wooden castle for me as a boy and I remember I really got in touch with my imagination there -- I was a sorcerer or I was a knight and because of the castle ... my mind would automatically go toward mediaeval things."

Another reason for taking on the role of the war-weary Crusader Behmen was a change of scenery from the stifling Louisiana interiors of Bad Lieutenant. Season of the Witch took the cast and crew to Hungary and the Austrian Alps.

"I wanted to be in nature, I wanted to be on a horse and in the snow and that's one of the wonderful things you can do as a film actor, you can literally just snap your fingers and be in another dimension and be in a forest."

BEST ACTOR OR WORST?

Cage and co-star Ron Perlman, of "Hellboy" fame, spend much of their screen time on horseback as they escort a young girl, suspected of being a witch and the cause of the plague, to a remote monastery where the action-packed denouement takes place.

The picture, directed by Dominic Sena, blends road movie and buddy film with supernatural thriller and period drama, and has critics wondering if it will be a hit or miss for an actor who divides audiences and exasperates even his most loyal fans.

"Since winning the best actor Oscar ... for Leaving Las Vegas, Mr. Cage has seemingly been choosing roles by throwing darts at a script-covered wall," wrote the New York Times in its cultural preview of the new year.

Cage shrugged off his fluctuating form.

"It's kind of exciting," he said. "It's exactly where I want to be, if you can always keep a little bit of mystery about it. If they can say in the same sentence that I'm the best and I'm the worst, then I think I might be doing something right."

Cage, part of the Coppola movie dynasty, is one of Hollywood's highest paid actors earning $28 million in 2009, according to Vanity Fair estimates.

But he is widely reported to have owed millions of dollars in unpaid taxes, has sought to dispose of several properties and was involved in a financial dispute with a former manager.

"I believe now that I can prove the phrase 'necessity is the mother of invention', because I've been very lucky to work with some very talented people," Cage said, when asked why he took on so many roles.

"(Season) I needed to do more than (for) necessity reasons, but because I genuinely connected with the ... material. But there's always that other element too, you know, as a result of what has happened that has been made very public."

(Reporting by Mike Collett-White)