Review of all 5 episodes:
This adventure has The Doctor, Jamie and Zoe arriving on a planet The Doctor has apparently visited before. The peaceful civilisation he knew is revealed to have had war in the past but is a pacifist society. They are attacked by two 'Dominators', from another world with their robotic henchmen 'Quarks' who intend to enslave those they consider worthy.
Unfortunately this is generally a below average adventure. The script by Mervyn Haisman and Henry Lincoln is pretty good and interesting but has not been executed well on screen. The writers actually withdrew their names from the production (releasing it under a pseudonym of Norman Ashby) and stopped working on the series altogether after the production team changed the story from a 6-parter to a 5-parter without consulting them and got Derrick Sherwin to write a new concluding fifth episode. This is very sad as their previous work on the series was tremendous. I do not feel this was ever anywhere near the standards of their earlier stories and did not need 6 parts but I think the script itself is better than the production makes it appear. The story's ideas are not bad but perhaps the production problems spoiled the end product a bit.
The acting of the guest cast is mostly OK but the direction is flat and the production is not well executed overall with terrible costumes, unimpressive sets etc looking too cheap and cobbled together, including the rather silly Quark robots.
Some decent standards are still in evidence in aspects of the story and the performances of regular cast Troughton, Hines and Padbury are very good but this adventure is a little bit dull and not as well produced as it should be at all. It is below what you want to kick off season 6, especially after such a great season 5.
My Ratings: Episodes 1, 2, & 5 - 6.5/10, Episodes 3 & 4 - 6/10, Overall - 6.3/10