It is difficult to imagine, from my perspective, how odd 'Mission to the Unknown' must have seemed to viewers at the time. It doesn't feature the Doctor or his companions, showcasing instead the Daleks, and whilst I am perfectly aware that it serves as a prelude to 'The Daleks' Master Plan', viewers at the time found a historical waiting for them the following week with no announcement to explain where the Daleks had gone. With hindsight, it is thus robbed of some of its impact, but nevertheless remains a gripping little story.
The Daleks are superb here. Whereas their last story made them objects of ridicule, 'Mission to the Unknown' restores them to their former glory. We learn that they are planning to invade the entire galaxy, which neatly continues the progression of the threat that they pose since 'The Mutants', but whilst this announcement from the Dalek Supreme is suitably chilling, it is Mark Cory's terse conclusion that if there the Daleks on Kembel the entire galaxy is threatened that really emphasizes how dangerous and powerful they actually are. Hearing them boast is one thing, but learning of their reputation from others is much more impressive. In addition, we immediately get an impression of their cunning; connoisseurs of Dalek stories past must surely realize that they are unlikely to make allies without planning to double-cross them, but here we see them leading a gathering of alien plotters, which instantly hints at bigger things to come. The Varga plants also serve to emphasize the nasty technology of the Daleks; genetically engineered plants that transform humans into mindless fellow Vargas are an unpleasant concept, not merely killing, but dehumanizing. They also show once more the Daleks' adaptability Â– having chosen a jungle planet as their base of operations, they employ a defense perfectly suited to this environment, making the jungles of Kembel almost as dangerous as their nearby city. The Planetarians, besides serving to hint at just how big the Daleks' new scheme is, do very little here due to time constraints with only Malpha getting lines. Nevertheless, they leave an impression thanks to some imaginative costume designs, which make them seem immediately just as alien as the Zarbi or the Rills.
The other main protagonists of 'Mission to the Unknown' are the three humans. With Garvey turning into a Varga plant as the episode begins, it is Cory and Lowery who are left to carry the compact plot, and their tense relationship allows the plot to unfold without seeming like forced exposition Â– Lowery is clearly first angered by Cory's killing of Garvey and then later terrified by tales of the Daleks, and these emotional responses are a catalyst for Cory's explanations of why he wanted to land on Kembel. Cory himself is every inch the noble but determined hero, who accepts that the lives of himself and Lowery are expendable, so long as Earth can be warned of the Dalek plan. Impressively, de Souza carries off the part whilst managing to make Cory seem resolute, but not inherently callous.
'Mission to the Unknown' is slightly let down by a rather silly plot device, which is pointed out by The Discontinuity Guide Â– Cory learns of the Daleks secret plans, because they broadcast them over a loudspeaker system. In addition, there are a couple of hints that Nation doesn't know the difference between the Universe, galaxies, and solar systems. Despite these niggles however, 'Mission to the Unknown' is an effective episode.