The Golden Amazon's Triumph by the late British author John Russell Fearn (
ISFDB,
Wikipedia,
SFE) is the 3rd novel in his long-running Golden Amazon series of vintage science fiction adventures starring a genetically-engineered superwoman of initially ambiguous morality, this installment seeing her commissioned to figure out who is spying upon the dealings of an interplanetary shipping company, and uncovering the lingering scheme of an embittered former V-rocket scientist who has apparently laid a terrible revenge plan using the capabilities of his invention, free for a limited time courtesy of publisher Endeavour Press' Venture imprint.
This was originally published in 1953 by World's Work, re-conceived from several pulp novelettes which appeared under the Thornton Ayre pseudonym (SFE says he changed her origin story), and apparently this series was very popular back in the day (and was a long-running feature of The Toronto Star Weekly), reprinted several times and running to no fewer than 21 original novels (and an additional 6 posthumous ones).

<-- closest we have to a Wonder Woman smiley, if Endeavour are doing this as a tie-in promo, which would be a nice touch
Currently free @
Amazon (available to Canadians & in the UK and pretty much everywhere else Amazon sells worldwide, since this is being done via their KDP Select exclusive-or-else program)
If you happen to like this and wish to read more, Endeavour have already e-printed a few of the other novels, which are affordably priced, and they frequently have generous 99 cent discount sales for much of their back catalogue as well.
Description
Chris Wilson, formerly chief of staff of World Airways, is now Controller of the Dodd Space Line, an interplanetary shipping company.
Mr. Rindle Emerson has come to discuss lunar ores, specifically itumen. Itumen is a special sort of ore found just below the Moon’s rock pumice surface. An extremely valuable resource.
Feeling very good about this proposition, Chris says goodbye to Rindle, but as he starts making calls within the company, he notices something strange about the huge cold-light globe hanging on a silver rod from the ceiling.
He is being spied upon!
But by who?
He immediately calls Violet Ray Brant, the supergirl whom the world knew as the Golden Amazon.
A woman of incredible intellect and bearing who would surely figure out what was going on.
It seems than an agent, by the name of Vanmeer X-19, had been recruited by Carl Mueller to feed information out of the Dodd Space Line.
But how was that possible? Carl Mueller had died five years previously.
After the Nazi’s were defeated, the V-rocket programme had been developed in all sorts of capacities, however Carl Mueller had been so bitter in his defeat that he had fired V-10#s from the moon to the Earth, loading their war-heads with atomic explosive.
To this very day the disappearance of Malta from the world, and the ruins of Cairo, Durban, and other great cities remained as monuments to his savagery.
Will Carl be successful this time?
Not if Violet Ray Brant, the Golden Amazon has anything to do with it…