The Tardis lands on a moving spaceship originally from Earth. The spaceship is orbiting the Sense-Sphere, home to the Sensorites. The Sensorites keep the ship in orbit around the planet. One of the crew members, John, has become insane through the ordeal, while the other two crew members Carol and Maitland seem resigned to their plight, and plead with The Doctor and his companions to leave.
This, however, proves impossible, because The Sensorites have removed the locking mechanism from the Tardis, trapping The Doctor and his companions on the ship.
Eventually, the Sensorites make contact with The Doctor, and it's arranged for him to travel down to the Sense-Sphere to negotiate a settlement with the Sensorites. It seems since the arrival of the explorers from Earth, many Sensorites have been dying due to an unknown disease. It's also learned that the Sense-Sphere was discovered to be rich in the rare mineral known as Molybdenum, and the Sensorites fear that the humans will return to exploit them in their quest to obtain the molybdenum.
Ian get sick after drinking some water at a reception. The water, which is what ordinary Sensorites drink, is found out to be contaminated with deadly nightshade. It seems that several crew members from the spaceship have survived and have been poisoning the water supply. Meanwhile, the City Administrator has murdered the Second Elder and taken his place, and has secretly been working with the survivors in hopes of eventually taking over as the First Elder.
The Doctor eventually lures the surviving crew members, who believe that they've been fighting a war with the Sensorites for years, out into the open. The plotting of the City Administrator is also revealed by the end of the episode. Maitland, Carol and John (having been cured of his mental illness by the Sensorites) leave for Earth, taking the insane crew members with them for treatment.
This whole story is a bit unusual for the time period, where most extra-terrestrials or obvious alien-like creatures were almost always viewed as enemies or at the very least, threats to humanity. In this case, neither side is wholly innocent and the story can't simply be viewed in simple black and white.
The Sensorites, and their leader the First Elder, are motivated by self-preservation and do not wish to be exploited by the Earthmen. However, their keeping the spaceship crew prisoner, and driving one insane, along with the actions of the City Administrator show that the Sensorites can be just as ruthless as the humans.
In the end, however, I found the story to be bogged down by a rather slow pace, much like Marco Polo was. There's nothing inherently wrong with a long Doctor Who story, if it's interesting and the pacing is good (a good example from this series/season is The Daleks). But the Sensorites seems to take forever to get where it is going, which robs the story of its rather unique aspect of featuring a race of all-too human aliens.
Coming next, the first series/season wraps up with The Reign of Terror, which I'll be reviewing next. After reviewing that episode, I'll be taking an overall look at the first series/season, particularly focusing on The Doctor and his companions and their changing relationship over the course of the series/season. Then it's onward to the second series/season with Planet of the Giants.
