Half way in, all spoilers.

Episode 5:

 The Brigadier comes in at the last moment, firing his gun at the alien. The alien turns to him and The Doctor tells him not to stop it. Another UNIT soldier runs in and the alien touches him, presumably killing him. The Doctor tells the Brig that someone is using them, they’re not acting on their own. The Doctor wonders if they’re being manipulated into thinking the aliens are here for conquest.

 The death of Quinlan seems to have made things harder – more red tape as everyone is jockeying to replace him. Cornish gets the medical report on The Doctor’s physical tests and The Doctor is very quick not to talk specifics – I’m guessing the whole two hearts thing, as well as other physiological differences. 

 Back at the chamber, the three aliens get a new dose. The one alien who was taken on the killing spree is very weak. Reegan brags to Liz and Lennox about what a great killing machine they are.

 General Carrington shows up at Space Control to forbid them launching; he says it’s obvious it’s the beginning of “an alien invasion with the collaboration with a foreign power.” The Doctor presses him, asking him why he is opposed to it. He never answers, just blusters and makes threats to go to the highest authority.

 Lennox leaves, bluffing the guard that Reegan has left behind with Liz’s help. He goes to UNIT but the Brig is busy and has him placed in a cell, since he’s reqeusted ‘protective custody’.

 The Doctor suits up for his trip in Recovery 7 (the radiation faded so they were able to re-use the capsule). The Brig is there to see him off in a scene that makes no sense whatsoever, unless it ties in later. (Not that the Brig seeing him off doesn’t make sense, but I don’t see why it was filmed, what the point was.)

 Reegan finds out Lennox has gone to UNIT and calls in to his superior. Reegan is told to take care of The Doctor while the other will take care of Lennox.

 Fueling continues and The Doctor is in the capsule, running through checks. Reegan sneaks into the launch facility, attacking a UNIT guard who stops him. Reegan fucks with the fuels or something, trying to sabotage the rocket.

 A guard brings Lennox some food, but it’s an open isotope! He signals the alarm in the cell, but the assassin has already cut the wire.

 The Brig, patrolling, comes across the guard Reegan attacked, who tells him what happened. The Brig sees the sabotage.

 The countdown gets down to the final ten, when the Brig arrives to demand they stop the countdown, but Cornish doesn’t react and the rocket launches. There’s too much variant fuel and the rocket is launching much faster than it should. The Doctor has to try to use manual controls, but they’re not responding. He tells them to jettison stage one prematurely, which explodes after separation. The rocket is at normal speeds now, allowing him to avoid going too far, eventually ending in the Sun.

 He achieves orbit, safely and begins adjusting the craft, seeking the Mars Probe 7. He links up with the probe ship. Suddenly, there’s a large unidentified object on collision course with the probe. He looks out the porthole and sees… I guess it’s an alien craft?… and the credits roll.

Episode 6:

 It is in fact, a space ship, one The Doctor says is enormous. He says he’s going to try to evade it. Cornish tells the Brig that he needs to conserve his fuel for re-entry. The Doctor sends a message that he can’t evade, but it’s cut off.

 The Doctor finds himself aboard the space craft – his capsule has been taken inside the ship. They communicate with him, telling him he is safe and to exit the capsule. He does so, stepping out into what appears to be a cave like environment (I wonder if it’s an organic ship) and is instructed to go to the light.

 Three astronauts sit watching a device, acting like they’re watching a game on telly. They obviously think they’re already back on Earth, in the Space Center on quarantine. When The Doctor tells them they’re prisoners in an alien spaceship, they laugh at him.

 There’s a musical tone and strange lights and all three sit down as if hypnotised. An alien appears on a wall, like a video screen. The alien looks like a mummy more than anything else and demands to know why they have broken the arrangement – if the Ambassadors are not returned, they will destroy the Earth.

 At Space Control, they’ve determined that it’s a spacecraft. General Carrington (who was on Mars Probe 6, remember) advocates to destory the alien ship, shoot it down, bang bang bang! Dominator Rago, I mean, Professor Cornish refuses to make assumption that the alien ship is a threat.

 Carrington goes off to recommend an all-out attack to the UN. He leaves, and the Brig tells Cornish that he thinks the general knows a lot more than he’s letting on – and brings up the fact that Carrington was on an earlier Mars Probe mission.

 The Doctor makes a deal with the alien to let him return to Earth and find the ambassadors and bring them back. After making the arrangement, the alien disappears from the wall and the humans return to normal. The Doctor says he’ll do what he can to get them out of quarantine and they ask for some food to be sent in.

 The Americans are planning to launch an unmanned capsule to observe the alien ship up close. Their launch is in six hours. The Brig tells Cornish that Lennox was murdered, and Dominato… I mean, Cornish begins a laundry list of all the things that have gone wrong on the Brig’s watch. So the Brig pulls out his gun and pumps two rounds in Cornish’s head. Hah, consider that my April Fools’ joke on you.

 Cornish DOES list all the things that have gone wrong – astronauts still missing (not sure what the Brig has to do with that one, though), Liz kidnapped, Taltalian killed and now Lennox. The Brig retaliates with a bunch of facts that emphasise that Carrington’s “foreign power” theory is full of bunk.

 The Doctor contacts them to let them know he’s on the way back, but will be radio silent until it is time for the landing instructions.

 Liz is in the chamber, bringing them another isotope. The aliens approach her and one of them removes its helmet to reveal what’s supposed to be an inhuman face, but it looks like a caveman with skin issues. She gets out, visibly troubled, and Reegan, who just returned from errands. He offers her a job, with the alternative of killing her and “buying another scientist”. Reegan gets a call and is instructed to go meet The Doctor.

 Recovery 7 touches down at the launching pad. Reegan has gained access, driving the van again and pulls some hoses out of the van, hooking them up to some pipes outside the “Decontamination Unit”.

 The Doctor is in the Decontamination Unit, getting dressed, as Reegan turns on the gas. He lays down while waiting for the okay to leave, when a smoky gas pours in and he passes out. With a gas mask (the funky ones the men wore in the helicopter) on, Reegan goes in to retrieve him.

 Security in this place is crazy lax, yo.

 General Carrington returns and tries to make The Doctor look to be behind all the troubles. Carrington asks all sorts of questions about The Doctor, but the Brig can’t really give any answers. The general says Geneva is still debating. He tells the Brig and Cornish the it’s a “moral duty” to “arm every missile with nuclear warheads and blast that thing out of the sky”.

 “I think the general’s a bit overwrought.” – the Brig

I think he’s insane.” – Cornish

 Reegan calls in to his superior, telling them that The Doctor is dead. He’s unconscious on the floor at the place the aliens are being held. Liz is there, and he wakes to see her. Reegan seems to be making his own plans.

 The Doctor rises and sees the aliens and confirms that they are aliens and that he has been on their ship and spoken to their commander. Reegan tells him if he can make a communication device, he’ll let he and Liz live. The Doctor sits down to make a list of components for Reegan to gather, while Reegan leaves.

 General Carrington shows up; it seems he’s the main bad guy, and he says since his instructions weren’t followed, it’s his “moral duty” to kill The Doctor and points his gun at him… and the credits roll.

Episode 7:

 Reegan shows up and argues with Carrington, telling him that they need The Doctor to build a machine to communicate with the aliens. Carrington seems to think this is a good idea.

 The Doctor gets the general talking; he reveals that this was a trap he set up. He met the aliens back on Mars, where they killed one of his crew with a touch. He’s convinced the aliens are planning to invade Earth. The Doctor plays along, agreeing to help. The general tells Reegan to ready one of the aliens, he has a specific need for it, then gives Reegan a list of isotope storages to raid.

 The American satellite approaches the ship but suddenly ceases all transmissions. It is believe the satellite was disintegrated.

 The Brig receives a call that Carrington’s men have captured an alien and they’re bringing it there.

 Reegan takes out the other two aliens, telling The Doctor he had better get the machine done by time he brings the aliens back. Reegan takes the aliens to a facility where they break in.

 General Carrington has brought the alien to the Space Control, to do a live telecast. The tv man asks if this won’t cause a world panic (but as we know, this would only suit the general’s needs.) The general intends to call upon the nations of the world to attack the alien spacecraft.

 The two aliens are back at their holding facility, and The Doctor and Liz are getting ready to test their machine. They mutter to each other about boosting a signal, so they’re up to something. Turns out they’re sending out a morse code SOS, which the UNIT troops (as well as all public service like ambulance, police, etc) pick up.

 Cornish confronts Mr. Wakefield (the tv man) about going through with the telecast for the general.

 The Doctor gets his machine working and Reegan grabs the mic from him, threatening the aliens with death if they don’t do as he commands. The aliens demand to know why they are being used to kill when they came in peace.

 The alien ship contacts the Space Control, threatening total destruction if their Ambassadors are not returned. Carrington is present and uses that to back up his beliefs. Carrington tells Wakefield to speed up the process for the world-wide broadcast hook up.

 The Brig gets a call about the SOS and tells Carrington he’s going to investigate. Again, Carrington accuses The Doctor of working with the aliens, and the Brig to boot, and has his own soldiers arrest the Brig.

 Carrington tells Cornish that he has taken control of the Space Centre.

 The Brig is being marched somewhere, but he beats up the two soldiers escorting him and grabs a car to leave. (HELL YEAH, YOU DON’T MESS WITH THE BRIGADIER!) He returns to UNIT HQ, where he finds out that the SOS was coming from old Army property near the Space Centre – the Brig quickly makes the connection to Carrington.

 They take Bessie (as all the UNIT jeeps are at the Space Centre) to the land. They see the delivery van that Reegan has used. As they pull up, two of Reegan’s thugs come out of the bunker entrance. There’s a firefight, then a REALLY BADLY choreographed fist fight between one of them and the Brig.

 I mean, really, really bad.

 The Brig bursts down, shoots Reegan’s gun out of his hand. After making sure everyone is all right, they haul of Reegan, but not before he suggests using the aliens to break into Space Centre and stop the general.

 There’s this really obnoxious mellow music that plays every time the aliens are walking around. It’s just stupid. The aliens force their way through the front gate.

 Cornish confronts Carrington who has him arrested. The telecast goes live with Wakefield introducing the general. The aliens arrive and the general shouts about being invaded and fires on the aliens. The Brig and his UNIT troops enter the room and the Brig tells Carrington that he’s taken the place and he’s placing the general under arrest. As Sgt Benton takes him off, the general feels the need to emphasise one more time that he had a moral duty to do what he needed to do.

 The Doctor tells Cornish that Miss Shaw will help him communicate with the Ambassadors, and all they need to do is return them to the ship and the human astronauts will be returned. He says his good byes and leaves… and the final credits roll.

 Not a great serial, not too bad. I think it could have been 5 episodes and been the better for it. Another “crazy man in authority” bad guy story. Not my favourite type of villain, but one very popular in the late 60s and early 70s, it seems.  (It seems there were a lot of rewrites on this and that contributed to a lot of the clunky, uneven pacing and writing.)