I found this serial utterly entertaining.  Sarah Jane is fun, Harry is a treat, it is good to see the UNIT crew a bit for one last time, and I just love the setting of Tulloch Moor.  It just felt like a nice, tight example of the base under siege trope.  There's lots of memorable characters, not just the returning UNIT figures like Benton and the Brigadier, but also memorable new individuals like the Duke of Forgill.  I think production did a good job bringing the energy of Scotland to the table and from there it is just a nice, consistent experience.  It's easy to enjoy something like this with the Fourth Doctor.  He's just so charming and there's a dynamic to how the show was structured at this time that made Terror of the Zygons a lot of fun to follow.  With it kind of being one of the last stories to feature UNIT for a good, long while, it feels like the end of an era.  So there's something very nostalgic and charming about this story.  The Zygons don't stand out much as monsters here but like everything else here - they do the job.  They very much fill the role of a classic, UNIT-era alien force to a T.  And I think in this case that really works to Terror of the Zygons' benefit.  Sometimes playing it to the formula, but doing a very good job at that structure and showing what works best about it.  A bit underrated, if you ask me.

Loved this story finally a good 4th doctor story to sink my teeth into

Season 13 has a phenomenal start with this rather unique story. The show starts with a not entirely accurate Scottish character, the stereotypes in this story are are knowing (writer Robert Banks Stewart is Scottish). It is a welcome relief to have the show set somewhere other than England - this show reacts well to change.

After three consecutive adventures with returning monsters (Sontarans, Daleks and Cybermen) it is refreshing to watch a story with the most successfully realised new monster since Spearhead from Space (though not quite trumping the Autons' debut). The actors playing the human forms of the Zygons deliver perfect performances in this. Sister Lamont is terrifyingly portrayed, her stare is still seared into my mind now (a fortnight after watching Terror) and mirrors the kind of wicked grown up who happily petrifies children. The Duke of Forgill is very sly and only slightly "off" in terms of appearing human. I feel genuine danger for Harry and Sarah Jane when they are unknowingly in the company of these wicked monsters.

When Ian Marter gets converted he tops these performances with his memorable and frightening attack of Sarah Jane in the barn. They both act this impeccably - Harry is a true menace and Sarah Jane looks genuinely scared in these scenes. Here they back up the assertion I made in my last review that (for me) they are the ultimate companions to The Doctor. It is both awful and exhilarating to see our favourite characters fight in this way.

The true form of the Zygons is equally successful, a rare accolade in Doctor Who. 42 years after transmission they still look brand new due to their unique design. Imagine how much more enjoyable Revenge of the Cybermen would be if the Vogans looked this good! Their spaceship is perhaps even more inventive in its design, the organic panels, controls and doors add a significant visual variety to the modern day(ish) UK setting of the rest of the story. Combined - these features make Terror of the Zygons the most visually exciting story since The Claws of Axos (though not quite trumping that either). Much of the visual success of this story must been down to legendary director Douglas Camfield.

The scene where The Doctor frees all of the human hosts from the Zygon's ship is impressive. We get to see the real versions of those poor abducted humans and the difference is immediately obvious, ingeniously written and well played.

The Doctor continues to have lots of exciting character moments, such as the scene in the decompression chamber with Sarah Jane where he puts himself and his companion in a trance in an effort to save their lives. He plays all this lightly with no drama, instead it is playful and exciting - without being hammed up or insincere.

It's been a whole year since we last saw UNIT. Robot felt like a Pertwee story with Tom Baker in it, Terror of the Zygons however has a spooky quality which seems to sit very well with Baker's curious and impish Doctor. Baker is very comfortable in the show and gives UNIT a fresh dynamic. I especially adore seeing Nicholas Courtney's Brigadier alongside the fourth Doctor, the same character who worked with the previous two incarnations of the characters - tying together otherwise disparate eras of the show.

Once The Doctor, Sarah Jane, Harry and UNIT solve the mystery of the oil rig (it was the Loch Ness Monster!) the story suddenly moves to London. This feels to a certain degree tacked on to the end of the adventure, although I found this forgivable as I wanted more and it helped keep up what was already a fast paced four parter. The ending might not be quite as good as the set up - but the journey was wonderful.

The big drawback of this adventure is that it marks the end of Harry's time as a companion to The Doctor. Whilst I know Harry will appear again later this season it does seem odd that he does not get written out in a brave, heroic or particularly interesting way. He simply chooses to stay behind at UNIT HQ. I will wait until the end of this season to determine whether I prefer the show with one or two companions.

At the end of this story I wondered which of the regular writing team wrote this excellent script. I was surprised to see that Robert Banks Stewart was new to the show (I wish he had more than one more remaining story lined up!)

Great story to start off Season 13. The Zygons and their spaceship and how fantastic they look probably make up for the couple of scenes with the Skarasen. While it maybe didn't go all the way with the shapeshifting concept, it's a great ending to the original UNIT era.

+1 for scotland, -1 for the horrible texture of the zygon's control panel