This novel, first published in 1965, was one of my favourites from the period and I still have my well-worn 1967 paperback. It's several decades since I last read it so I thought I'd see how it stood up today.
I've already posted one review of a novel by this author (A Trace of Memory, reviewed 15 December 2007) which I started as follows:
"Keith Laumer (1925-1993) was a prolific American SF author who specialised in fast-paced adventure stories (of which the Bolo series, concerning intelligent tanks, is best known) and comic satire, notably in the Retief books about an interstellar diplomat. A Trace of Memory, published in 1963, is a stand-alone novel in the former category."
A Plague of Demons falls into the same category, being a short (170 page) and exciting adventure thriller. It is set on a near-future Earth and features a government agent, John Bravais, who is tasked with investigating the mysterious disappearance of large numbers of soldiers involved in the formalised battles then being used to settle disputes. He observes a dog-like alien - one of the demons of the title - decoying soldiers away from a battle and attacking them. He is able to kill one of these extremely tough creatures and take back evidence of its alien origin. His task then becomes the investigation of what is going on, and to assist him he is given a new programme of internal biomechanical enhancements which greatly increase his strength, endurance and survivability. The demons are quickly on his trail, assisted by their ability to manipulate people's minds so they can appear to be ordinary humans, and what follows is a running battle which ends up off the Earth as Bravais desperately tries to fulfil his mission against heavy odds. I can't say more without spoiling the surprises for any new readers, but I will say that this is the book whose popularity inspired the Bolo series.
The story is told in the first person with the laconic hard-boiled style of a Mickey Spillane thriller, including one-liner gems such as: "I was as weak as a diplomatic protest". There is also something of the flavour of Eric Frank Russell's novel Wasp, reviewed here on 26 August 2007. The introduction in particular reminded me of the start of a James Bond movie - I could visualise the film scenes as I read. In fact, the whole book would make a good film, with little need to change anything. Inevitably, the complex plotting and character development which feature in most modern novels are notable for their absence, but in this kind of story they would only slow the pace.
I was intrigued by a couple of scenes for a personal reason. In one of them Bravais, having just received his enhancements, breaks the machine used to test his strength. In another, he is able to use his mind (in this case aided by radio) to analyse and overcome electronic locks. As I read these I realised that I had included similar elements in my novel Scales, without being aware that I might be borrowing them from somewhere else. This isn't the first time this has happened to me and does make me think about the process of imaginative writing. Clearly, our imaginations are developed from and informed by our own experiences and previous reading, and it can be difficult to determine which are our own original ideas and which are those we might subconciously have recalled from a consciously long-forgotten story.
Anyway, to return to Laumer: I can well understand why I liked this book so much and can warmly recommend it to readers who enjoy the style and pace of these 1960s SF thrillers. It's such great fun, with an added dash of nostalgia!