If the last episode saw the departure of Jo Grant, the episode The Time Warrior witnesses new opening credits (some elements of which carried over into the more famous Tom Baker credits) and the arrival of a new companion who would remain one of the most popular of all time, Sarah Jane Smith, eventually reappearing on the new series in addition to K9 and Company and her own spin-off series, The Sarah Jane Adventures. It also introduced the Sontarans, who have remained popular and made recurring appearances on Doctor Who.
The episode involves a Sontaran who has crashed on Earth in the past and who is kidnapping scientists from the future (when the Doctor is on Earth and working with U.N.I.T.) in an effort to repair his spacecraft. The perennial theme of science wrongly perceived as sorcery is to the fore at many times. The crash landing Sontaran ship is viewed as a “falling star” and thus an “evil omen.” Another major theme is the relationship between weaponry and morality. The Doctor says (in response to the provision of more advanced weapons than were available in that time) that advancing weaponry outpacing advancing morality would be a disaster. It is debatable whether this stance makes sense, except in the broad sense that advancing technology can cause great harm when there are no strictures of morality present to constrain its use. But surely advancing morality should not be expected to go hand in hand with the development of ever more efficient methods of killing others.
Another great quote is from the Doctor: “A straight line may be the shortest distance between two points, but it is by no means the most interesting.”
You can watch part one of the episode here:
And for K-9 and Company, check this out on YouTube: