The 5th Doctor and Nyssa arrive on the planet Mondas and discover a population eking out an existence below ground; a situation which will see the beginning of the Cybermen.

Nyssa meets the Hartley family and witnesses their daughter, Yvonne, become a proto-Cyberman. The Doctor meets Thomas Dodd, a ‘spare parts’ black marketeer and the earliest Cyber forms.

The planet Mondas is dying and the Committee is processing humans into Cybermen to allow them to survive on the surface of the planet. Despite the Doctor and Nyssa’s efforts, the humans trudge inexorably towards their predestined fate – to become the Cybermen.

The Doctor is horrified when Doctorman Allen, the creator of the cyber process realises that his alien physiology could be the answer to the problems she has been having with humans rejecting the process. Against his will she includes her findings in the process meaning that all Cybermen are, in part, based on a template of the Doctor.

However, the Committee eventually loses all vestiges of humanity and the processed Cybermen begin to take charge; their cold logic defeating the cries of even Doctorman Allen, who finally realises the terrible mistake she has made.

The Doctor and Nyssa succeed, however, in destroying the Committee – now the Cyberplanner – and the Cybermen’s commander, Sheng. They leave Mondas presuming that, if nothing else, they have given the Cybermen a chance to coexist with the unprocessed humans and that Allen is planning on reversing the processing as far as possible, allowing the Cybermen to at least experience some emotion.

In their absence, we discover that Sheng is still alive and that the humans are doomed after all…

As Lance Parkin states in A History, the dating of Spare Parts is difficult as there is little in the story itself to suggest when this occurs relative to Earth.
The Doctor states that Mondas’ technology is millennia ahead of Earth, therefore implying that although the setting and characters reflect 1950s Northern England (all planet’s have a North), this is merely an affectation for the purposes of storytelling; giving the drama somewhat of a post-World War Two vibe.

The Doctor does state that, due to the Committee’s decisions the planet is ‘stuck in the 1950s’ suggesting that were it not for the cybernetic enhancements to their population, the Mondasian culture would be millennia ahead of Earth in technology and culture, seeing as their ‘1950s’ has occurred whilst Earth humans are still little more than apes.

A History suggests that this story occurs somewhere between 65,000,000 BC and 12,000,000 BC. The planet begins its journey back to our solar system at the end of this story and Parkin suggests that, as this will not take as long as the journey out due to the propulsion system, that the Cybermen may well pilot Mondas around the Universe before re-entering out Solar System in 1986 as seen in The Tenth Planet.

It’s interesting that in this ‘prehistory’ section of the Universe’s history, it is the 5th Doctor and Nyssa who seem to be witnessing many of the events (both real and, in the case of The Boy that Time Forgot, artificially created). They have visited Jurassic Earth, witnessed the destruction of the dinosaurs, visited an alternate prehistoric timeline and now, have seen the early days of Mondas. Looking ahead, they will also visit the distant past of Nyssa’s own planet Traken, in Primeval.

Spare Parts is simply put – superb. It is the ultimate tragedy. As listeners, we know exactly what the Mondasians will become and to see it painted for us with human characters who you really care for, brings home the horror far more than the origins of the Daleks in Genesis of the Daleks ever does. Peter Davison and Sarah Sutton are brilliant in one of their best performances as the Doctor and Nyssa. The personal level of seeing the beginning of the Cybermen so soon (relatively) after Adric’s death hits home and the contrast between the Doctor’s initial desire to leave Mondas to its ultimate fate and Nyssa’s determination to fight against it happening makes for some passionate scenes. The guest cast are note perfect, particularly Sally Knyvette (of Blakes 7 fame) as Doctorman Allen and Paul Copley as Mr Hartley.

It is quite possibly the ultimate Cyberman story and will stand as, not only one of the best stories that Big Finish have produced, but one of the best Doctor Who stories of all time.