US paranormal drama series Supernatural has become a cult hit since it first hit TV screens in 2005.
Sera Gamble is the supervising producer and writer on the show.
She discussed what it is like working to a TV budget, the impact of the writers' strike - and why writing horror is so much fun.
Warning: This story contains plot spoilers.
Describe Supernatural and why horror and sci-fi fans should tune into it.
Jensen Ackles [l] and Jared Padalecki [r] are the stars
Supernatural is the scariest show on TV. If you like movies where you're squeezing your date's hand the whole way through then you'll love the show. It's scary, funny and emotional.
In every episode we try to hit harder than the last one. It's different to other shows like Ghost Whisperer and Medium because when our characters find a ghost, they don't talk to it - they shoot it in the face.
What is the feel of the show?
It's deliberately shot like a late 70s/early 80s 'B' horror movie. It's filmed in Vancouver, Canada which helps set the moodiness because it's nearly always dark and raining.
Tell us about the lead characters Dean and Sam Winchester played by Jensen Ackles and Jared Padalecki.
The show is about blood and gore but the central core is about the close relationship between brothers Sam and Dean. Jared and Jensen own those roles now and they are as sweet as they are handsome. The show really started when they were cast.
What was the continuing storyline for seasons one and two?
Season one was all about the boys searching for their father John who had gone missing while hunting the evil thing that killed his wife. Dean went and got Sam out of college and he was dragged back into the world of demon hunting.
In season two it was more about the mystery surrounding Sam and the physic abilities he seemed to have been given by the same demon that killed his mum.
And how did the Hollywood writers' strike affect season three?
Season three was shortened from 22 episodes to 16 because of industrial action. The strike was hanging over our heads for a while and we were just waiting for the trigger to be pulled and then we would all go home. By the ninth episode we knew we were about the stop so we were scrambling to finish scripts. We had to re-order some episodes.
What was the mythology for season three?
Season three was about a demon war and how to create a full-scale conflict on a TV budget and without a cast of thousands. It also was focussed on a deal Dean made to save Sam which meant he only had a year to live.
In the end that storyline was the one with the biggest pay-off and the most juice for both characters so we went big on that idea.
How did you get the job as writer on Supernatural?
It was what we call "staffing season" and my writing partner Raelle Tucker and I were called in to talk to the show's creator Eric Kripke. I felt qualified to work on the show because when I was 12 I spent the summer watching the entire horror section. I'm doing the job that I always wanted to do.
How long does it take to write one episode?
It takes a few weeks because of the process you have to go through. You start with one or two paragraphs and that gets sent to the studio for approval. Then you break it out which means putting it onto a whiteboard. The outline is sent to the studio again. Then if it's approved you have about two weeks to write the script. It's fun torture.
What's going to happen in Season four?
Season four is going to be awesome. I can genuinely say that I am so excited about it because there are so many stories to explore. Dean is in hell, Sam has had to live without him for a while and one of the new characters from season three, Ruby, has a bigger role to play fighting alongside Sam.
The season three finale of Supernatural will be on ITV2 on Sunday 29 June. Sera Gamble talked to BBC News reporter Karen Rollins.