An excellent story, 4/5! Heavy spoilers throughout.

I'll start where my heart lies - with the thoschei content! (Okay, and my general Master character thoughts, but, you know, thoschei!!)

The Master gave a very convincing performance as the Doctor; if I hadn't known MacQueen was in this and pretending to be the doctor before I begun listening, I would have believed he was the doctor, 100%. I like how the characters themselves pointed out that the fact that the Master was so good at pretending to be the Doctor, pretending to be good, that this goes beyond deceit - some of it must be real. Admiration, connection... love? Specifically where Klein pointed out how much the Master enjoyed helping UNIT, not just faking that enjoyment... yeah, that was the stuff right there. She gets it. I do genuinely love when we have characters within the story who are doing the same thing as the audience, expressing our feelings for us - it feels interactive. Usually characters' decisions and observations invoke feelings in their audience, but this time, it almost felt the other way around - or as if we were having a conversation, sharing our ideas. I suppose that's what comes of a story written by fans!

When the Master reveals himself and is taunting the Doctor after not killing him, his voice goes soft, almost purring... Thoschei fans stay winning (: loved all the nods to RTD-era thoschei too! The way 7 growls the Master's name is so many levels of insane. Plus, the classic "Join me, let's rule the universe together" offer my beloved!
"My dear dear dear Doctor" eeeeee us Thoschei fans really were fed with this one! A little fanwanky, but hey, that's what I'm here for. Despite all this, there was a line implying that the Doctor and the Master were brothers. It was very jarring amongst what did seem like an intentionally romantic depiction of their relationship, but I suppose that it's likely that as a thoschei fan, I was reading that into the audio more than was intended.

Now, let's give at least a little bit of this review over to the other characters and the plot - as much as I'd like to, I can't only talk about the Master!

Despite not knowing anything about Raine, I found it easy to understand her personality and motivations. I feel like I should have listened to more Klein material before this, as there were definitely a couple times where I felt I was missing references, but I still understood the story perfectly well. Generally speaking, I found myself caring about even the most minor of characters - I started crying on the tube when the Tolian attacked Sylvie, I was so attached! I do get more invested in the emotional side of stories than most people, but I still think anyone would enjoy the level of thought and work that has been put into developing each and every character in this story.

This audio uses UNIT very skillfully; we are really made to feel for the soldiers, actually form relationships with them as an audience - not something the TV show usually succeeds at doing for one-offs. In the interviews, they mentioned that they tried to make this not just a doctor/master story, but specifically a UNIT story, and I think it shows. They did that well.

The interviews were great fun to listen to, I do recommend them. Loved Maynard's actor giving a shout out to all the ensign expendable UNIT soldiers who've died over the years, and people talking about how lovely Sylvester is to work with, including of course his spoons!

Over on the plot side of things, I was not very engaged by 7 and Raine's parts in the first couple discs, as I often felt that the characters were giving us the information rather than us learning it ourselves. It was as if this was written for a visual medium, rather than a purely auditory one. I especially noticed this when the giant floating heads came into the story - it just did not feel like something that had been written to be heard, rather than seen. However, the plot and characters were strong enough that this did not bring the audio down as much as other audios written this way, which is why I only dropped one star off the rating for this.

The general shape of this story was quite similar to sound of drums/last of the time lords - the master disguises himself as someone else, recruits a dying alien species he somehow "saved" turning them into weapons to be his army, and begins taking over while keeping the Doctor prisoner and threatening his companion. It's a little derivative and a little fanwanky, but I did enjoy it a lot. I am very much a fanwanky person - I enjoy shout-outs and namedrops and nods and references and shipping fuel. It can sometimes overwhelm a story and take away from the plot, but I am just one of those people who really likes that kind of stuff, so it does not take away from my rating at all. I can understand how people who aren't in it for the references would be rolling their eyes in this story, though.

(As an example of a reference that got me squealing, when I heard "Terserus", I went "omg!!! Planet from my Curse of Fatal Death!!!" (Not realising it's appeared in other Who media too)).

There was never a point where I was bored - the pacing was good and I stayed engaged in the story without feeling lost at any point. This was something I was quite worried about, considering the unusual length, but they really pulled this off!

Overall, a wonderful story that definitely lives up to the hype with commendable development of even the most minor of characters. An incredible introduction to a brilliant Master that well deserves those four hours, and those four stars! I recommend this to anyone with a long car journey coming up who needs a good way to pass the time! I promise, you won't regret it.