Would of been stronger if it had less episodes. Still, it's another good one for the third Doctor, Jo and the UNIT regulars. The Master is present as he's still stranded on Earth. But it's really the machine that's the villain.

There are some fantastic moments in this serial. The checkers scene where both the Doctor and Jo shush the Master, the moment when the Master panics because he thinks he killed the Doctor for real, Jo getting to be brave and clever in her own right, the overacted fight scenes are fun, and both Benton and Yates are great.

However. The plot has FAR too many aspects so that they all sort of get lost: the dangerous effects of the machine, the hostage situation in the prison, the peace conference being hijacked by a hypnotized Chin Lee (who also doesn't get enough on-screen time post hypnosis), the stolen missile used to threaten a third world war, and Barnham wandering around all innocent because he no longer has his evil impulses. It's just too much, making it almost easy to miss that some of it doesn't make sense: the machine takes out "evil impulses" but then the mind grown from that causes people to see their worst fear and then, somehow, literally die from that fear (not the fear itself but whatever is the cause of the fear, ie actually drowning). At first it seems the evil impulses have just imbued the machine with sentience, but then it turns out that somehow a nearly-impossible-to-kill living creature has grown from them. The Master's entire plan is "start a war that decimates the Earth," which on its own would be amusing and I wouldn't mark down, but with everything together it's one more thing that isn't fleshed out.

The story doesn't even have TIME to get into the problematic and eugenicist issues with choosing to (or even having the ability to) remove evil/criminal impulses from a person, beyond a couple throwaway lines at the beginning.

I’m one of this serial’s biggest defenders.  It’s the last gasp of the Season 7 style of storytelling, is the final contribution for both Don Houghton and Timothy Combe, the latter barred from Doctor Who for going over budget, and actually sees UNIT be an international organization.  Despite being set in the UK, this is one of those classic Who serials that feels incredibly global, the parallel plots of Stangmoor Prison, the peace conference, and transporting the missile really creating that.  It’s also fascinating for how it engages with the international community, care is taken with the script to not paint the Chinese characters as exotic caricatures and keeps the language as close to correct as possible.  Chin Lee as a character is genuinely compelling despite being a victim of the Master.

Roger Delgado as the Master gets to really make this fascinating second impression, while it has similar setup to Terror of the Autons with the character making an alliance, as the serial goes on Delgado relishes the chance to seeing what the Master deeply fears.  The same can be said with Jon Pertwee as the Doctor, his fears reflecting his experiences in Inferno and the evils he has fought and can no longer face due to his exile.  Katy Manning is always a delight with Jo getting to be in the middle of the prison plot while Nicholas Courtney once again excels in the action sequence near the end of the serial.  Dudley Simpson being promoted to essentially the main composer also adds leitmotif.  Truly an underrated gem.

This was a very fun story! But I must say, the Master's plan was very weird. He's stuck on Earth because the Doctor stole his TARDIS's Dematerialisation Circuit last episode. So the Master, instead of immediately making a plan to, you know, steal the thing back, makes a (needlessly, but that's the Master's prerogative) very complex plan to start WW3, so that he can rule the Earth in the aftermath. Was he just resigned to being stuck here forever? He only gets the circuit back at the end because the Doctor suggests an exchange, the circuit for the missile, in their negotiation. A win for the Master, sure, but out of sheer dumb luck being on his side rather than his plan actually working.

Moving on to Jo: I love her already, even though the "companion as a literal assistant to the Doctor" is not my favorite dynamic. She's just so charismatic that it works. And she got to kick some ass this time! I really like how kind she is to everybody, and how she has Benton and Yates eating out of the palm of her hand. Speaking of them, both my boys had their own little arc going on in this story, which was great to see. The Brigadier was a delight as usual. As another reviewer said, they really are becoming a little family.

10/10 for the Doctor's outfit in this one, I must say. Loved how he got to be cheeky for a bit in the beginning (waving at the camera, interrupting that guy's presentation while sitting as flamboyantly as he possibly could on that plastic chair, speaking Hokkien with the Chinese delegation and leaving the poor Brigadier just sitting there). All of his interactions with the Master (no comment, I cannot not like the Master) were great as well. That little part where the Master is worried the Keller machine killed the Doctor, and when they are working together to destroy it were both very good at showing that hey, these two really were close at some point, uh? And that final phone call? Mwah, chef's kiss.

Jo beating the Doctor's ass at checkers while the Master patiently watched was so funny. Specially with the Doctor seeming to be genuinely mad that he lost, complaining that the game is "too simple" for him, and he prefers 3D chess (Star Trek reference!?). Jo/Doctor scenes I thought were great were he telling her random stories about his travels, and that exchange where, during UNIT's takeover of the prison, the Doctor makes a little joke about the hostages being in danger, forgetting that he and Jo *are* hostages; she just looks at him and he goes "...Ah" after a while. On this note, damn, UNIT sure killed a whole lot of people when they took the prison back, eh?