The plot is fairly straightforward--a man invents a machine that is used for horrible doings, and seeks to correct the misdeeds. The machine in question here is the titular dueling machine, which allows men to enter the imaginations of another and fight to the "death." In the dueling machine, death isn't the end, however, it's just a defeat--the problems start when the machine starts killing people for real.
It's sort of amusing now to think of such a device that ISN'T used for explicitly sexual purposes, when inventions such as this have been thrust forward largely by the sale of pornography (home video, internet, e-readers), but whatever. The novel requires a great many conceits to imagine that, okay yes, this machine works, and it somehow has replaced all-out war, because through the lens of this narrative, disputes between countries can often be boiled down to disputes between men.
It's sort of an imperialist outlook on history, isn't it? Great men, and all of that. One of the protagonists is even referred to as hopefully becoming a "great man" in a few years at the novel's end.
I don't know the actual efficacy of such a device as the dueling machine. If you could have Chamberlain and Hitler sit down in this machine, theoretically, would it have really stopped people from frothing at the mouth to fight for very long? It's the kind of notion that can only truly work in a science-fictional world where resources are plenty and economic unrest seems non-existent, because as far as I can tell, most wars are, at their base, about land and resources how to get more of them--not ideals.
And what's odd is that Bova seems to acknowledge this; the main thrust of the discovery arc of the protagonist--Dr. Leoh--is that he wants to find a way to transfer men to more planets, so they can have more land and resources and stop fighting all the time. I suppose the idea is that most men and women don't even understand that what they're really pissed off about is not having enough, so they get stuck on ideals and petty feuds? Anyway, the dueling machine is recognized by Leoh as a stop-gap measure, even in the book.
All told, it's an odd little book. You've got space Nazis--the antagonistic force--without all that horrible business of fascism and genocide (or at least, none that is really explored), with just strong hints of tyranny and strong examples of military discipline and a mad leader, enough to make the analogue of Nazi pretty clear. Turns out, that's still pretty evil even without the genocide. (I suppose they could just as easily be Space Stalinists, or the Space Khmer Rouge [besides that not existing yet at the time of publication]. Humanity is sort of depressing in its ease of analogues for tyrannic evil that way. But "Space Nazis" is just catchier.)
It's sort of neat that the main protagonist here, Dr. Leoh, is an old man. He is a fun character, highly fascinated by science and discovery, but prone to long tangential excursions into exploring his own fame, showing off his dueling prowess in his machine, daydreaming about younger women, and being cranky with politicians.
There's a complicated relationship with gender, here. By complicated, I mean "problematic." And by complicated and problematic, I am trying to be diplomatic about saying it is pretty awful. There is a grand total of one female character in the book, Geri, and she runs through the motions of being a trophy, and then manipulative via feminine wiles, and then a trophy again--all of this without any of her point-of-view in a book with frequently shifting point-of-views. There is literally more time spent in the point-of-view of men who die within five pages of their first appearance than there is in the point-of-view of a woman who is present throughout the entire book. That's kind of crap.
If that wasn't enough, in the last few pages of the book, the main antagonist--an assassin named Odal--ends up in love with Geri as well.
"He," meaning Odal, here, "had expected to feel either an excitement at the thought of pleasing Geri, or a new burden of fear at the prospect of returning to Kor's hands. Instead he felt neither. Nothing."
Yeah, me too, buddy. I understand what Bova was going for with that, I think, attempting to indicate a sort of disillusionment by Odal of his own failing status, but I think it's sadly a bit too revealing of where the reader is at this point in the novel as well.
All throughout, the writing is crisp and easy to follow along with. There are parts of this that I found silly, but at the same time it all moves at such a fast clip that I was compelled to keep going. Pages fly by, full of information and conflict, and all of it engaging. Recommended for a fun read and a cross-section of societal opinions in the sixties; just don't go in expecting anything earth-shaking when it comes to convention or worldview.