The last Dave Martin script! Feels like a milestone given that with Bob Baker he made a whopping 8 serials - few writers on Who have had more screen time. Perhaps apt then that this really *feels* like a series finale in the modern sense, wrapping up our journey with the key to time. Their first script, The Claws of Axos, still stands as by far their best unfortunately, but this story is one of their better ones. Merac’s psychedelic experience at the hand of Lalla Ward’s character nicely calls back to Claws. Baker and Martin often have those cool, very visual, druggy looking scenes.

An interesting revelation comes in part 3, when the twin planet that the army has been locked in a war with is in fact home to only one entity - an emotionless robot that has been running the whole show on behalf of a shadowy master. There are some neat concepts at the heart of the story but sometimes in the process of getting to those points you have to sit through some fairly workmanlike, serviceable but not particularly exciting plotting.

The time loops in this story are a great idea - but you spend probably 2 minutes of running time watching the same loops again and again. That countdown gets dull. Drax, the time lord who spent many years in Brixton reveals Douglas Adams as the script editor - it’s a fantastic idea but I do wish his character had been bedded in a bit better with more time on screen.

I love that K-9 gets his hero moment with Drax and The Doctor jumping out of him at the end in their miniaturised form. Lovely to see Lalla Ward with K-9 - pointing towards an exciting new era.

I’m not sure the whole “key to time” thing adds up to much in the end. It was disbanded as quickly as it's pulled together but was a good mcguffin to tie the series together. About as meaningful as “bad wolf” anyway. This series was not quite as good as Tom’s first three but was a huge step up from season 15.