First of all, I didn't listen to any previous solo Benny audios, this was my first. And I understood everything. All you need to know - Benny has a son Peter, and she is in a conflict with Brax.
Now, what about the audio?

It was really good. Not a masterpiece by any means, but still an extremely enjoyable audio that kept me invested throughout its entire runtime.

Benny was great here. A lost mother trying to get back to her son. Her fear for Peter works great here, as even if time travel is (almost) her speciality, she is still scared for her child and wants to find him by any means necessary.
But even when she gets her usual "Benny stuff" to do, she quickly switches from flee to fight and stands her ground. I love Benny so much.

Mycroft Holmes, played by late great David Warner himself, was also great. A less eccentric version of his brother, yet equally smart. As the villain of this story says - "Your brain is the closest this era of humanity has to an advanced CPU."
Mycroft helps Benny a lot and even with his mind being somewhat limited by the era where he resides, he isn't confused by an advanced enemy and still manages to somewhat deduce what they are capable of, which is always appreciated after a ton of stories where really smart people see an alien and suffer permanent brain damage.
Also, I'm a big fan of Benny and Unbound Doctor audio stories, so hearing Lisa Bowerman and David Warner together in one audio is always appreciated.

Peter Miles as Straxus was just brilliant. If his name sounds familiar, then you are correct - that's his debut, and he will go on to appear in the Eighth Doctor Adventures.
This incarnation of Straxus isn't very different from his other selves, but still feels unique because of mainly two reasons.
1. Peter Miles's performance. His voice isn't particularly threatening, but it is strong enough to imply that there is more to his character than meets... uh... the ear? His voice is great and manages to give just enough mystery to get invested into this version of Straxus.
2. The lore. I will talk more about it later, but the lore used in this story is presented with just enough mystery to intrigue the listener and thus have the direct "appendage" of that lore in the form of Straxus to grab you and throw you into this new and very less-known version of Doctor Who Universe.
Listen, I love Straxus, and I'm always up for more content with him. Not a perfect Time Lord as he wants everyone to perceive him, but a very interesting character.

Simon Kingsley as Septimus is also great.
From the moment he appeared I realized that the voice he makes sounds familiar. And it was true - he was copying Chris Cwej's voice, and for a good reason, which I will explain later.
Simon manages to greatly portray two versions of the same character - one calm and one insane (although the calm one later also turns out to be insane, but you get the picture).
Even if his character is insane, you understand his logic. You don't exactly sympathize him, but you understand the way he thinks, which in my opinion is a great way to write villains - make them not sympathetic, threatening, dangerous, but just explain the logic behind what he does.

And now, it's time to talk about the lore, because ooh boy, it is great (and also the reason I decided to listen to this audiodrama in the first place).
This is the closest we get to the lore of Faction Paradox being present in the Big Finish version of canon.
Before that they quickly shoved the VNAs and the EDAs into an alternate universe, but eventually they grew fond of those, and elements of the lore were incorporated into BF's vision.
This audio has lore elements of both VNAs and the EDAs, and introduces them greatly.
First of all, why does Septimus sound like Chris Cwej? And why does Benny mistake him for Chris when she meets him in person? The answer is easy, he is a Cwej - a mass-produced biomechanical clone of the original Chris Cwej, created by the Time Lords.
Second of all, what were the Cwejen made for? For War in Heaven. This war isn't names directly in this audio, but Straxus does mention a war his "people" are waging.
And that's what I love about this audio. It introduces these elements, yet very cleverly avoids usage of terms a casual Doctor Who fan knows very well, making this audio feel like one of those unofficial unlicensed Doctor Who spin-offs (like Faction Paradox for example) - we don't hear the word "Time Lord" here, or the name of the Doctor being dropped, but the way the characters talk while implying those words is so simple yet you instantly recognize what they are talking about.
The lore of the War in Heaven is mysterious on its own, and I LOVE what BF did to it here - bringing it into its vision for just one audio and not giving everything away, making it just mysterious and interesting enough to make the listener invested and want to learn more. That's authentic to that lore itself - it is very obscure.

Long story short - great audio for introducing the previously ignored part of the Doctor Who universe, but making it just mysterious enough not to give too much away yet keep the listener entertained.

This is a fine episode. Benny is fun as she always is, and the idea of her meeting Sherlock Holmes sounds fun in theory. And I'm sure, if Victoriana and Sherlock are things that appeal to you, you would enjoy this episode a great deal, because it is absolutely full of Victorian atmosphere and tropes.

Unfortunately, I find that dull as ditchwater.

As I say, Benny is a highlight to me, as she always is. But this episode is long, chock full of weird 'period typical' sexism which for some reason modern writers always feel compelled to force into Victorian period fiction, and tediously boring as far as investigations go. I think, mostly, this one is just not for me. Even when it turns into aliens and SF-ness, it's still mostly just Benny and the aliens talking and talking and talking.

Benny wants her Time Ring back. And then she gets it. And it takes us an hour and fifteen minutes of tedium to get there.