Where in Fenspace is "Dr. Asmodeus Grey"?

[Star Ranger4]

I think they developed it from some "quick-learning" device some other Fen invented.

Correct. Specifically, it's a development of the sleep-learning device that was invented by the unfortunate cab-driver who became Tabitha Doe.

So, given that Tabitha is the first and best known of the victems, it would be safe to say that now only Dr Gray know how it works?
Hear that thunder rolling till it seems to split the sky?
That's every ship in Grayson's Navy taking up the cry-
NO QUARTER!!!
-- "No Quarter", by Echo's Children