AAA3 - Spearhead From Space 3

The Doctor-UNIT alliance unofficially begins in this episode, with The Doctor making use of his TARDIS homing device (never to be referenced in t his form again) to work his way back to UNIT headquarters, meeting Liz Shaw, and getting to work on analyzing the shattered remains of an Auton sphere. He also tries, and fails, to fly away in the TARDIS for the first time, but certainly not the last. Robert Holmes adds another chapter to the enduring legacy of The Doctor here, too. In addition to giving The Doctor a second heart in the previous episode, Holmes also introduces the concept of post-regenerative amnesia, which has been a feature of most of the subsequent regenerations seen since then.

Let's take time to mourn two aspects of Doctor Who that appear in this story but seldom do again afterwards. One - the jazzy score by Dudley Simpson. This story sees the penultimate Simpson score before his transition to de facto full time composer on Doctor Who, which, unfortunately and coincidentally, saddled him with an awful synthesizer for him to work on exclusively for Season 8, after which his scores never really did recover. Whereas Simpson's scores had a sameness to them for most of his time on the show after this, his Season 6 and 7 scores are remarkable in their uniqueness.

The other thing that we see in this story but rarely again are agile monsters. The Autons are seen to run at quite a clip, either in retreat or in pursuit of their target. It might be the fact that this story is shot entirely on location and therefore there's actual room for them to be able to run long distances than the confines of BBC Television Centre would allow. Whatever the reason, just think of all the slow, lumbering aliens in the years to come after this that somehow managed to catch up with their prey, and remember a time when you literally had to run for your life to escape an alien threat.