This is one of my favourite classic series stories.
Producer Graham Williams, was brought in to take over from Philip Hinchcliffe in the face of growing concern from the likes of Mary Whitehouse that the programme was becoming too dark and violent for children.
It's somewhat ironic then that this story is thematically one of the darkest in the entire history of Doctor Who.
It's fair to say that this was a transitional period for the production team, so the (most welcome) darker tone owes a lot to the writing style that had gone before, this can also be explained by the circumstances at the time, when Terrance Dicks was asked submit a new story as a quick replacement for a planned vampire story, which would have clashed with the BBC's adaptation of Bram Stoker's Dracula, due to air around the same time.
Filming was also affected when the studio scenes had to be moved from BBC television centre in London to Pebble Mill studios in Birmingham.
Tom Baker's working relationship with Louise Jameson took a turn for the better during the making of this serial, known for sometimes being a prickly personality, Tom was very close to Elisabeth Sladen who played previous companion Sarah Jane Smith. His attitude toward Louise Jameson was at best frosty to begin with.
In the commentary featured on the DVD Louise Jameson says that she feels that their relationship turned a corner when filming a scene in which Tom was meant to enter the shot on cue, he would deliberately walk in ahead of his cue and upstage her. She asked for the scene to be restaged three times in order to get it right, and subsequently earned Tom's respect.
I think Terrance Dicks' contribution to the programme is often overlooked, his stories may be more simplistic compared to some of his contemporaries, but they have a sound structure, which is one of the reasons I find this story to be one that I go back to again and again.
My pick of the guest cast would be Colin Douglas as Reuben, his demonic smile when he is playing the Rutan is chilling.
This story is also notable as one of the few classic Who serials directed by a woman, Paddy Russell, and what a sterling job she does too.
The extras on the DVD are up to the usual high standard including; a commentary by Louise Jameson, John Abbott and Terrance Dicks, a documentary about Paddy Russell, a documentary about collectable memorabilia, and my favourite of the collection, a documentary about Terrance Dicks.
If you have yet to see a story featuring Tom Baker as The Doctor then I would rate this as one of his best.