How come Captain Magenta isn't involved in the manhunt?
How come Scarlet doesn't sense the Mysteron mechanic?
How come the Mysteron mechanic can be killed with a bullet?

who said he was dead - he might of just bben very badley injured

I was always thought Magenta was in another radar van in a completely different area so missed the whole thing entirely. Perhaps, of course, he was on standby in Cloudbase should the Mysterons take advantage of the situation and threaten someone else..

Symphony (I think it was Symphony but stand to be corrected) really makes a fist of things here. Not only does she land when she shouldn't have, but after she's been irradiated and put in the pursuit vehicle, why didn't she crash it a lot sooner? She said later that she'd never driven one before which implies that she had some sort of (albeit lousy) control of the vehicle rather than it being on some kind of autopilot. So why didn't she try crashing it as soon as she could so that Spectrum could find out it was her rather than careering off down the road and giving Captain Black a chance to get away?

If the only reason why Captain Black let her out of the radioactive room was to give himself the opportunity to get away, why did he say to her "The Mysterons can also show compassion"? She'd know the real reason soon enough.

I did like the constant bleating of Lt Green begging Colonel White to let him go down.

Personally I think it was an attempt at a 'everyone laugh' moment at the end of the episode (like on the Original Trek), although in reality I can't see this happening (I mean, this is the best of the best of the worlds security) and she lets Black get away so she could go on a joyride? She should be chucked out of the service straight away!
As to the compassion line, this episode was very early on in the series, so perhaps this was an idea of Black's humanity still existing (although it was eventually submerged by the Mysteron influence). Alternatively he had initially planned to kill her, and then the idea struck him about using her as a decoy - after all, he wasn't expecting her to land her plane in the first place. Then he thought of the decoy plan, and let her go (saying the compassion line to lull her into a false sense of security so she would think he was being kind) and we all know what happened.
In retrospect, there is one new puzzle; why can't Black just use get the Mysterons to transport him away like (I believe) in 'Inferno'?

How come Black escapes from the centre without anyone noticing at the end? They all race off after an SPV, while Black takes his sweet time cleansing himself of the radiation (which the power station staff FAILED TO NOTICE OR CALL SPECTRUM ABOUT)
We see Scarlet, Ochre, grey, blue, and some guy in a room at the power station just as Black radiates Symphony. Next time we see them, Scarlet Ochre and Blue are at the gate, and Grey is back in his radar van parked at a house he was at earlier, and its suddenly daylight again!

And back to this oft-nitpicked ep.
Scarlet needs to go back to school judging from some of the phrases on his report, e.g
'There was no Mysteron activities'

Also when Colonel White compelments Scarlet and Blue for their loyalty to Spectrum they both say " Thank you sir." but Ed Bishop's voice comes out of Scarlet's mouth and Frances Mathews voice comes out of Blue's mouth.

So. Scarlet knows the garage mechanic is a Mysteron. How? Does he use his strange sixth sense? No. Does he see the body of the original mechanic? No. Does he see a gun in the mechanic's pocket? No. The mechanic doesn't ask for I.D. OK. So if the person in charge of the SPV had been an elderly woman suffering memory loss and a very bad case of flu and just had plain forgot, Scarlet is perfectly entitled to gun her down?

But would an elderly woman suffering memory loss have been allowed to be a Spectrum agent in the first place?

Well, probably not, but the point is that forgetting something like that seems an easy thing to do, yet Spectrum agents can kill anyone they even remotely suspect of being a Mysteron?

And this elderdly woman could have been in Spectrum for 20 years or something. I don't think people could just resign or be laid off from Spectrum.

At this point, Spectrum is less than a year old. As an international policing force, they would demand the highest standards.

Scarlet said he expected the mechanic was a Mysteron when he didn't ask for their ID so Scarlet got his gun out ready to fire if necessary, the mechanic pulled the gun out which put the final piece in the puzzle.

When Symphony drives out of the Atomic Centre in the SPV, should that building on the right wobble the way it does?
The guards wobble when she crashes into the tree at the end of the chase sequence.

One of the guards that finds Harris has Lt Green's gun, even though Green never uses a gun in the series.

When the car is crushed with the mechanic in it, notice that the roof of the garage appears to buckle. So garages in the future will not only be understaffed, but they will also be made out of cardboard.

When Symphony moves back away from Black saying
"No...no you can't do it." you can just see a human hand holding her left arm.

It surprised me that Captain Black let Symphony go at the end of the episode, but I guess killing her wouldn't have done anything for the Mysterons.

This episode was the first time that they had proof that Captain Black was under the control of the Mysterons. (Captain Scarlet had no memory of the "conversation" he had with Black in the first episode.) How did Black get back to Earth, anyhow? Was he teleported there? Did he return in the Martian probe ship?

That scene where the mechanic dies has to rank as one of the nastiest death scenes in the series. Possibly in the entire Supermarionation opus.

Did Symphony deliberately drop that medallion? Just in case no one noticed her Angel Interceptor parked in the clearing?

BTW, do the Angels carry weapons? I've never seen anything resembling a holster on their flight suits. If they're not armed, that makes Symphony's actions even more idiotic.

The rear-faced seating didn't do much for Symphony, did it? Of course, if she'd been wearing a seat belt....

At the end, Symphony tells Col. White: "I'm sorry, sir. I feel that I let you down." Well, yes, Symphony, you did. With a resounding thud.