Iterations of I written by John Dorney and directed by Ken Bentley

What's it about: The house on Fleming's Island had been left to rot. Ever since a strange and unexplained death soon after it was built, and plagued with troubling rumours about what lurked there, it remained empty and ignored for decades until the Cult moved in. As twenty people filled its many rooms, the eerie building seemed to be getting a new lease of life. But now it is empty again. The cult found something in its corridors... and then vanished. Trapped on the island one dark night, the Doctor, Tegan, Nyssa and Adric look into the building's mysteries, its stories of madness and death. Their only chance is to understand what terrible thing has been disturbed here... before it consumes them utterly.

An English Gentleman: He finds it is always better to adopt a positive approach to life...or a delusional one! The Doctor is quietly very smug when his companions cannot do a better job than him in landing the ship where they want to go. It's not as easy as it looks. Paradoxically he doesn't like to speculate but he does like to hear the local superstitions. You only have to be wrong once when the ghosts come out to play. The fifth Doctor is beautifully written throughout this story, giving lie to the fact that he has become a biege blur on audio in the past couple of years (there is an argument to be made for that, but this is a very good counter-argument). He's incisive, witty, self-deprecating, insulting, resourceful and very intelligent and Peter Davison responds to the stirring material, giving one of his best ever performances. The Doctor defeats the monster of the week with a calculator - just wonderful.

Maths Nerd: Adric refuses to acknowledge that he has piloted the TARDIS incorrectly because equations never let people down. It always disturbs me when Adric and I agree on something and his mis-pronunciation of Sinead is one such instance (I also have trouble with Siobhan and Aoife). The Doctor wishes for once the little git would just do as he's told.

Mouth on Legs: Tegan's experiences in steering the TARDIS towards Castrovalva have taught her not to tinker around with the console anymore. This story must be set after Black Orchid where Tegan has decided that she would like to stay with the crew for a while. That's nice because it means this box set offers two alternative versions of the character from season nineteen, the grumpy one who has just had her life turned upside down and the calmer one who has adjusted to her life aboard the TARDIS. For Tegan to suggest that somebody else is being negative is quite a statement. She finds the sea air quite invigorating. She's the sort of woman who would risk saying that a day cannot possibly get any worse...and suffer the consequences. I really enjoyed Tegan in this story, she has a fair amount of attitude but for the most part she is intelligent, observant and understands that she needs to do what she is told in a crisis. She admits that she has her own problems with the Doctor but listening to him is usually the safest option. The Doctor is touched by that, and by her decision to stay with him when she could scarper away from this horror and back to her old life. Tegan smartly reasons that ever creature has its weaknesses, you just have to ration out what it is. The I will go for the loudest and most obvious target...can you imagine who that might be? Her capacity to find things to complain about never ceases to amaze the Doctor.

Alien Orphan: It's nice that Nyssa is a party to Adric's subterfuge to fly the TARDIS whilst the Doctor is distracted by Cranleigh's book. It feels like there are a pair of naughty school kids attempting to take the controls whilst Dad is busy with his head in a book. Like her collapse in Four to Doomsday, Nyssa is still susceptible to psychic attacks. Adric thinks that concentrating on light electronic engineering is exactly what Nyssa needs to take her mind of things. Surely she cannot be that square? The sooner Tegan introduces her to trashy soap operas the better. When the Master killed her father it destroyed her, ripped out her heart but she had to get on with her life. You never forget the pain.

Standout Performance: Bizarrely I found Waterhouse's delivery a little more difficult to get a handle on in this story, he really seems to be stressing the 'Adric of peace and light' voice that is supposed to be as authentic a representation of his voice in the 1980s as possible. I'm not sure I would have bothered with the affectation because he sounds far more like he did back then in the special features when he is just talking normally. Interestingly, it is during the scenes where Adric is called upon to react to things suddenly where the ethereal whispering drops and he slips comfortably back into being a teenager again. It's great to hear some Irish accents in Doctor Who, it is a brogue that we don't hear often enough outside the latest eighth Doctor series.

Sparkling Dialogue: 'I? Why I?' 'I didn't know you were from Newcastle...'

'Like a scream without a face...like insanity walking.'

'I wasn't aware I had tuned into The Open University.'

'It wont come out with the most sophisticated language in the world' 'Well that's aright, we understand Tegan. '

Great Ideas: I like the fact that there is a fair amount of set up before we catch up with the regulars in this story, setting up the narrative before allowing them to join. Before the Doctor, Adric, Tegan and Nyssa even set foot on the island it is given an appropriate amount of ominous build up. After that set up, the first episode is almost left exclusively to the regulars, proof if it was ever needed that these four characters could hold up a story on their own if the setting and the narrative were strong enough to highlight them at their best. This deserted home on the island with whispering voices and eerie psychic energy wafting about is potent enough to generate a tense atmosphere (even the Doctor states that lights are definitely a priority). There was always something very season one about Davison's first season, trying to recapture the idea of the Doctor kidnapping somebody and trying to take them home unsuccessfully and having the stories form one long narrative with recaps at the beginning of each adventure. So it feels very authentic for Iterations of I to separate the Doctor's party from the TARDIS to allow the adventure to roll on, the ultimate season one feature. Fleming bought the whole island as a wedding gift for his wife but she died during a party held at the house. After Sinead O'Connor's death it was impossible to sell the house on until the cult approached the owner, looking for somewhere cheap and secluded to set up shop. A cult that worships numbers? Again I can imagine Bidmead getting the ultimate hard on about that. The imagination is one of the greatest tools we have, says the Doctor and I couldn't agree with him more. A cult trying to break down the base code of the universe, what an incredibly dangerous thing to even hypothesise. Imagine what damage you could do if you reduced the entire universe to a malleable equation? Diary extracts (be they written, audio or visual) is something that I have seen used ad nauseum in fiction (it is particularly favoured by Justin Richards in his novels) to explain away the outcome of a traumatic event that the Doctor and company have stumbled upon. You can generate some real tension by slowly revealing what has happened before shining a light on the fact that the horror you are witnessing in the document is still present.  People breaking down into numbers - Dorney has a real talent for producing some stunning imagery. If something is trying to kill people it doesn't need to do so in a different way each time. Iteration is a process of trying to achieve a result and making various attempts at different methods until you get it right. It is isn't trying to hurt people it is trying to talk them but it is so different from mammalian life that it doesn't realise it is killing them with each attempt. A life form so different that just saying hello in various ways causes mass murder...that's terrifying. A sentient number. How has Doctor Who not covered this before? Such a simple concept and yet highly imaginative when applied in such a way. When it found itself caged it latched onto I, the most impossible number of them all. It is the square root of minus one, not irrational, just imaginary. Numbers only exist in relation to other things, you can't reach down and pick up a two, only two of something. Enslaved, the I could change and affect all numbers. You could use it to manipulate any computer systems you wanted. You could go beyond computers too, change the reality of the world. If a peaceful numeric creature can evolve then why not a predator. I could imagine the I attacks being realised in much the same way as the Keller Machine in The Mind of Evil, that grainy negative effect.

Audio Landscape: The sound design really struck me as being very strong in the first episode, Fool Circle convincing me completely that I was listening to a lost soundtrack rather than something that had been assembled long after this era was first transmitted. I also found the sound trickery when people were affected by the I to be quite disturbing to listen to, a genuinely chilling audio experience. Kudos to Fool Circle for their distinctive work on this story. Computer print outs, white noise, seagulls, a cliff face crumbling, waves crashing, a storm brewing and breaking, rattling a door handle, the generator coming to life and the lights coming on, rain running from a roof, a scream, whispering voices, computer equations tinkling away, Aiofe's dying screams, helicopter blades, shooting, a helicopter crash.

Isn't it Odd: A shame that the end of episode should lack any tension whatsoever after such an incredible establishing instalment. Tegan presses a button a keyboard, an act that is given an astonishing amount of importance given we have no idea what it will do. In places this story did remind me of ...ish but where that was a more intellectual exercise this has a unique sense of horror all of its own. You could perhaps argue that the climax descending into action after three episodes of intelligent discussion is a little easy but I thoroughly enjoyed the quicker pace of the final fifteen minutes (especially Adric proving himself physically and the crash).

Standout Scene: It is strange how something so ordinary, the repeated use of the letter I, can be made to sound so spine tingling when placed in a different context. It is a great motif because it comes with a sense of creeping horror, informing the audience that something is very bad is about to happen.

Result: 'I think our number might very well be up...' What a cracking first episode, atmospheric and haunting and landing this TARDIS crew in a chilling horror movie setting of the sort that the series lacked during its nineteenth year. This is another skilfully structured piece assembled by John Dorney with plenty of clues scattered about in the first two episodes for the careful listener to slot together to build up a picture of what happened on the island the summer previously. However even the most intelligent of listeners couldn't have foreseen precisely where this twisting storyline was going and once the cat is out of the bag about the nature of the threat I was both horrified and dazzled by the potential and complexity of the foe. Whilst Adric and Nyssa are served well, it was the handling of the fifth Doctor and Tegan that really impressed me. The dialogue is sharp and appealing and both Peter Davison and Janet Fielding respond to it by giving a pair of fantastic performances. I truly wish they had been this engaging on screen together but it is wonderful that the potential of this pairing is finally being realised. Where Psychodrome had a point to make by establishing the season nineteen team as a unit that can generate decent stories, Iterations of I is simply a cracking good story in its own right and would be regardless of the which regulars had landed here. Beautifully paced, packed with clever ideas and twists and with an atmosphere of dread that is hard to stop listening to, this is very good indeed. It's been a long time since I have given two back to back scores this high but this fifth Doctor box set has raised the quality of the year exponentially and the stories have been specifically tailored for my tastes. Between them they have been smart, funny, surprising, characterful, atmospheric and challenging: 10/10