The Paradox Planet written by Jonathan Morris and directed by Ken Bentley

What's it about: Whilst travelling in the vortex, the TARDIS is struck by an advanced war machine - a Time Tank! Losing Romana, the Doctor and K9 pursue the Tank to Aoris, a world quite literally at war with itself. Soldiers from the future are attacking the past of their own planet - gathering resources and stealing endangered species. But the past is not without weapons of its own - leaving deadly devices ready to trigger many years ahead after their enemies have been born. Trapped at opposite ends of a temporal war, the Time Lords have two time zones to save. But who is in the right, and who in the wrong? And when history itself is against you, can anybody actually win?

Teeth and Curls: The Doctor is attempting to learn to play the fiddle but Romana thinks it sounds more like he is trying to torture a small rodent. He thinks he is very musical but he's learning to play from a book that is geared towards octopoid lifeforms. There is an especially nice chemistry between the Doctor and K.9 in this story that manages to capture the relationship between Tom Baker and John Leeson despite the fact that it is interaction between Time Lord and tin dog. A sense of two older actors loving the fact that they are recreating the roles that made them famous. Romana sees the Doctor as her companion and something of a blunderer.

Noblest of them All: In real season seventeen style, Romana is deposited into her own plotline, essentially taking on the role of the Doctor for the story. As a result she is more sophisticated and cutting than ever, assessing the situation in seconds and passing judgement on it. She never carries a gun because she finds they have very little defensive value. As a Time Lord she obeys a rule of strict non-intervention...when it suits her. Romana almost enjoys leading the past selves up the garden path, promising them time travel but instead destroying any headway they have made in that field. She's devastatingly witty and I use that description with precision, if you are caught in the wake of her wit it is a devastating experience.

Standout Performance: Tom Baker and Lalla Ward seem much more confident in this story than they have in the first two stories of this season, but then it is a much more confident script so that is hardly surprising. They both get a strong role and a good dialogue. Any story that sports Simon Rouse and Tom Chadbon has got to be worth a listen. Neither of them has a role that is as compelling as the one they played in their televised Doctor Who stories but both acquit themselves well regardless.

Great Ideas: Another craft trying to materialise in the same space as the TARDIS. After the stresses of a similar situation in The Pirate Planet you would think that the Old Girl would have some kind of safety system in place to avoid this situation now. An expeditionary force, sent back through time to fight their own ancestors - you can always count on Jonathan Morris to come up with the good, meaty concept and crazy season seventeen ideas are something of his specialty. Any alterations to the timeline could have catastrophic consequences for the future, which is why they have been ordered not to kill anyone. Of course the same does not work the other way, their ancestors don't have to worry about causing any ontological paradoxes. Being at war with your descendents is a very peculiar state of affairs. Given the right conditions, Xenox crystals can warp the fabric of space time. How do you go about fighting a war like that? Sending a bomb down a mine shaft that lays inert for 1000 years, a time capsule rigged to explode. An explosive message to the future. They know the rough location of the bunker that the enemy will live in in the future and unless they surrender, they will detonate. Preferably they would like access to time travel, to send soldiers into the future and attack their enemy outright. Waiting a 1000 years to make an impact and never knowing if it worked is hardly a swift method of genocide. How nice to see the cause and effect of the bomb, Romana in the past seeing it being activated and the Doctor in the future when it is due to take off. Unfortunately the Doctor has to deal with the situation because he is strapped to the bomb. The past selves do not want to live up to their future selves, living underground, scavenging in the ruins of a once great planet. Why do I get the impression that this is a future that they have themselves created. Sending troops back through time to gather endangered species and bringing them to the future - now there is an original conservation project. Why do I also get the impression that the mass extinction of several species was caused by the future selves. Both the past and future selves have criticisms of the other side when this conflict is probably to blame for the flaws that they see in each other. Drang has a plan to remove the pollutants from the sea and air and to restore the planet to its former glory.

Audio Landscape: The horrible musical stylings of the Doctor learning the fiddle, a time drive breaking down, a dimensional incursion, the time ship materialising, ship powering down, K.9 trundling out of the TARDIS, woodland sounds, creatures concealed in trees, cocking a gun, gunshot, a ticking bomb, the menagerie.

Musical Cues: Jamie Robertson once again captures Dudley Simpson's reliance on simple instruments in a melodramatic style. He does this and manages to make the score feel contemporary too, propelling the action forwards. Bravo.

Standout Scene: K.9 emerging from the bomb that he has laid dormant in for 1000 years is such a gloriously unexpected and funny solution to disarming it.

Result: Very season seventeen in all the best ways, The Paradox Planet is the best 4DA in some time. It captures both the feeling of a show that is running out of money (the future setting being set within a bunker underground) and one that has a universe sized imagination that is desperate to burst forth (the high concept central idea and the creative narrative turns that spill from it). I've said it before and I'll say it again, the ingenuity of Jonathan Morris seems to be limitless and he has scored another winner with his script for The Paradox Planet, a timey wimey (when did I start using that phrase so casually without disgust?) romp that skips time zones merrily and has great fun with the idea of a planet that is at war with itself in different periods of its history. It's not a story that builds to much of a climax but then there is still half the story to go, the second cliffhanger might be a doozy but it comes completely out of left field and requires a lot of explanation in Legacy of Death. It's a boldly plotted story told in very entertaining terms and whilst it probably could have been plenty more serious (it is dealing with a war after all) it aims for the comic jugular instead which suits the era perfectly. Romana takes on the Doctor's role, she's the serious one. The Doctor is mostly having fun, which again feels authentic and Tom and Lalla are on fine form and backed up by an impressive guest cast. I'm pleased they will all be back next month because I am certain there is much more to learn about these characters. The same goes for the situation, I'm sure there is a manifest of twists and turns to come, these complicated Morris stories usually do. As set up, this was extremely enjoyable and with a powerhouse of an idea behind it like that it is a 4DA that made me think more than pretty much any other: 8/10