For those of you who have not delved into the parallel universe that is Doctor Who confidential, it is an episode length making of that is aired after Doctor who on BBC3 in the UK. I am unsure whether is aired in the countries (may be some one can let me know by way of a comment).

The Wasp and the Unicorn is a particularly special episode as it is a Doctor Who murder mystery!

But this is no ordinary murder mystery, it is based around the very real disappearance of Agatha Christie in 1926, when she vanished for 10 days and later returned with no memory of what had transpired.

Such an episode has some unique challenges in comparison to other episodes, as the director Graeme Harper highlights one by explaining that having so many main characters each shoot had to have several takes in order to get enough close ups of everyone in order to not give the mystery of who the killer is away.

The car chase during the episode appears to be at break neck speed, but the 1926 vintage cars can only go at a maximum of 20 miles per hour and as David Tennant points out, when it hit a hill the engine did not want to know.

This is well worth watching..

Further information and watch live on BBC iPlayer