Roots: Besides Bovril (via Klein's olfactory sense) The "Vril" more subtly share their name from Edward Bulwer-Lytton's Vril, the Power of the Coming Race, and also name check the conspiracy-based pseudo-historical Nazi society and the (also pseudo-historical) VRIL Nazi UFO project. The name of the nerve gas agent is presumably an ironic tilt at further conspiracy theories surrounding Klein's real-world counterparts.
Goofs: The climactic end-music as the Vril colony reasserts itself seems to turn briefly into the B-52's 'Rock Lobster'.
Dialogue Triumphs: "Doctor, your big bright future has fascists in it!" "Oh Klein, if you're interested in fascists I'll arrange a date with a Dalek."
Continuity: The Vril are a communal winged insect species broken down into various utilitarian types: workers, watchers ('doorkeepers' of the colony), warriors (the unfertilised 'default' class), healers and male drones which the Doctor never sees. Typical of many communal insects at the top of their hierarchy is a fertile queen, or 'Authority', as she is known by the Vril. At the centre of the colony and in a Hatching Yard the Authority lays thousands of hard-shelled eggs in a geothermal pool of bubbling hormonal fluids which cure the eggs and, depending on whether these are fertilised or not, the resulting pupae become warriors or workers. A further 'royal jelly' (though it is not named as such) can be used by the Authority's will to produce a new Authority, as with bees. The Vril communicate through smell and do not have individual names. Their numbering system is base eight (presumably representing their six legs and two mandibles)
Geopolice are an environmental agency enforcing the solar system and likely others. Charged with selecting and if necessary restricting access to planets across the various neighbouring systems identified for colonisation or exploitation they have a feared reputation and are apparently incorruptible. The organisation Stefan and Jackson work for is unnamed (it's possible there were only a handful more than themselves on the planet); they are raiders seeking the Vril's protein fluids, having almost devastated the Vril colony with the use of a 'Spear of Destiny' biological weapon akin to nerve gas.
It is implied that 'Vril' is the equivalent of Bovril in Klein's timeline (see 'Roots' - certainly the irony isn't noted by either her or the Doctor). Thanks to the TARDIS' translation circuits she 'hears' the Doctor's voice as having a "stuffy Prussian accent".
The Doctor's spare key outside the TARDIS would appear to be missing (c.f The Angel of Scutari)
Links: Power of the Daleks (the planet Vulcan)
Location: A Vril colony on an unknown planet within a system "high above the galactic plane" overlooking the whole of the Milky Way. So outside the Milky Way then.
Untelevised Adventures: The Doctor and Klein have already visited a number of uninhabited universal marvels, including Florana, the crystal plains of Mandroxya, the Folly Ocean of Quindrax IV and the mercury swamps on Vulcan (see: Links) - although it's possible he may have just shown them on the scanner.
The Doctor recalls past beekeepers he has known, including Aristotle (who "was always wittering on about them") and Thomas Jefferson (whom the Doctor met at a tea party), but curiously not Gorowny from Delta and the Bannermen
The Bottom Line: "This whole forest will talk to you if you just use your nose"
On one hand a more modern and more sophisticated version of The Web Planet. On the other, an exploration of individual versus group psychology (presumably a running theme in the Klein trilogy) but with insects instead of people (or alien birds) There are no easy answers, thankfully, in Jonathan Clement's story of individuality, ethics and questionable 'fascist' labels. The 'eco-nazis' are as stupidly human as any other character, and no more alluring a prospect to an unrepentant Klein than they are any more sympathetic next to the pathos of the dying Vril; easily the best realised of Big Finish's insect races. You'll hiss when Klein inevitably draws the rug out from under the too-trusting Doctor's feet, but it's all in aid of a stunning final act...