TV & Radio
Three young women, who look like they are straight out of some hip teenage television show, have set out to rescue London's teenagers from evil forces.
Brynne Larson, 18, and sisters Tess and Savannah Scherkenback, 18 and 21, from Arizona, are not the idea of a Hollywood scriptwriter but "real" exorcists on a mission.
They believe that every country "has a specific kind of demon" and Britain is a hotbed for "witchcraft" because of the popularity of J K Rowling's Harry Potter books.
"It has been centuries in the making, but I believe it came to a pinnacle with the Harry Potter books," Savannah Scherkenback says in the trailer to BBC documentary Teen Exorcists.
"The spells you are reading about are not made up," her sister added.
"They are real and come from witchcraft."
Larson said: "Harry is using this magic for good, so here we have the dangerous idea that you can use this magic for good or bad, whereas in reality all magic is bad because you're getting your power from Satan."
The girls, who all have black belts in karate, have vowed never to read the Harry Potter novels and hope to help British teenagers to rid themselves of "inviting Satan to possess them by reciting the spells in the Harry Potter books" as well as "sexually transmitted demons".
British film-maker Dan Murdoch has spent six months with the trio for the documentary.
He followed them to Ukraine and then to London, where they held an exorcism meeting under the guidance of Larson's father (and their trainer), the Rev Bob Larson, who says he has performed more than 15,000 exorcisms.
While he sees himself as a freedom fighter for God, sceptics say that he is preying on the vulnerable in a bid to sell his books, DVDs and "crosses of deliverance".
He does not see anything wrong in demanding money for his services.
"Money and motives; any time someone is in God's work it always comes up," he said.
"People will pay thousands of dollars to go to drug rehab or to pay psychiatrists, but there's this idea that spirituality needs to be for free.
"The average megachurch pastor in America; it's not uncommon for them to make up to $1 million a year. Well, I can assure you we are nowhere near that."
According to Larson almost half of the population is ruled by a demon.
Discussing his documentary, Murdoch said he had doubts about the team's demon-smiting mission.
"I don't believe in exorcisms after doing the documentary but I do believe in the power of belief after what I've seen," he said.