The Doctor and the other mannys who were shot are not dead, only having sleeps. Kellman doesn't get shot by cybermannys because he is on their side. He tries to help them by searching the Doctor's pockets to look for clues, but he only finds jelly babies and other Doctor noms.
Harry and Sarah meet Tyrum, who is still being played by Kevin Stoney even though he is wasted in this role when he could have been in much better parts in much better stories around this time. He was in I Claudius the year after this was made, and I doubt he got the part of Thrasyllus on the back of Revenge of the Cybermannys. Harry and Sarah fill Tyrum in on the plot up to this point.
I don't know why Harry Mailer, the Doctor and the Commander are sitting like monkeys in this bit, maybe they did it for lols or to confuse the cybermannys?
The Doctor tries to find out the cybermannys' plan. He provokes the cyberleader with lines like
"You have no home planet, no influence, nothing. You're just a pathetic bunch of tin soldiers skulking about the galaxy in an ancient spaceship."The cyberleader gets quite emotional and hits the Doctor, but it is a trick so the Doctor can steal one of their cyberbombs. This doesn't get him far though, as another cybermanny sneaks up on the Doctor and captures him again. Even though his escape attempt has failed, the Doctor continues to troll the cyberleader even as he is being told their plan.
"Our calculations indicate that two bombs, placed in the central fissure of Voga, will fragmentize the planet."
"Fragmentize? Oh well, I suppose we can't expect decent English from a machine."
Clearly the Doctor has been to the future and seen the internets.
The Doctor, the Commander and Harry Mailer are made to wear the cyberbombs and are sent down to Voga. The cybermannys that go with them are attacked by aliens but the cybermannys' pewpewpew guns are too powerful for the aliens and they go
Kellman teleports down to Voga and is captured by aliens. It turns out Kellman is a double agent, he knows about Vorus's rocket and wants to blow the cybermannys up too. He tells Tyrum about it and tries to get the aliens to work together against the cybermannys.
Kellman goes off with Harry to try and stop the cyberbombs from blowing the planet up, while Sarah escapes and teleports back to Nerva.
The Doctor, the Commander and Harry Mailer are still wearing the cyberbombs because they will explode if they try to take them off, and they are on a countdown to explode anyway! This makes for an exciting and suspenseful scenario, just the sort of thing that Terry Nation would do (as often as possible). They are trying to find a way to escape from the bombs when a lot of rocks fall on them.
Harry and Kellman are nearby and rocks fall on them too. Kellman goes
Harry finds the Doctor having sleeps, and he goes to take the bomb off him. Harry doesn't know this will make it explode - oh noes!
This is a big improvement on part two, with more happening and much better pacing. The Doctor's scenes with the cyberleader are good, as is the ratcheting up of the tension over the bombs. Because they don't explode (in this episode at least), the cyberbombs are being used in the Hitchcockian 'suspense v surprise' style, and are very effective as a result.