Adam Hall is the careful, meticulous, and patient author of the interesting character/spy, "Quiller". The series of unorthodox novels built around Quiller are extremely odd, as far as espionage fiction runs. 'The Quiller Memorandum' (first in the sequence) was published in 1966 and it was just not common at that time, for an author to make a point of flaunting his own genre's conventions. But his "Quiller" --a cynical and jaded free-lance agent--does just that. As rogue-ish as Len Deighton's 'Harry Palmer' (but not as sardonic), Quiller is a character type not seen repeated until something like Charles McCarry's modern 'Paul Christopher'. World-traveling and multi-lingual; quick reflexes, but definitely a loner, a "thinking man's spy".
What you really have to applaud Hall for is his setting out with a deliberately antithetical and unique notion of what a spy can be and do. Quiller--a shrewd, cerebral individual--is one of the few spies in the violent post-WWII era who refuses to carry a gun. Instead, he trusts his acumen and his resourcefulness to give him advantage. Though he's a solidly well-built agent with a high pain threshold, able to withstand rigorous abuse--more than this, Quiller is simply so thoroughly seasoned by his past wartime experience that guns are rather superfluous to the real business of spying which--as Hall suggests--relies far more on observation, perspicacity, and insight into the psychology of your opponents. Quiller can often see the next move of his enemy before his enemy makes it.
The first Quiller novel--a brooding, spooky affair--is not a snore-fest, though. There are sharp bursts of action which, refreshingly, Hall brings out slowly, as the result of a stomach-sickening and nerve-wracking build-up. Its not Alistair MacLean's style of zesty, energetic dust-ups every few pages; (all of which the hero recovers from in just a few moments). Creativity and realism both reign here: Hall accurately writes about physical brutality the way it really is: clumsy, pointless, and wearying; with throbbing painful after-effects that linger and follow one around. Its part of a general level of ugly harshness and roughness in Quiller's world which he does his best to avoid; and an important key to his character. Quiller is tired, disgusted, bruised, battered. Barely hanging on.
What drives him..? Well, he's not LeCarre's George Smiley wanting to "do his part for those who went before". He's more in the camp of a Jonathan Hemlock (Trevanian); who sees no particular merits on either side of the detente' conference table. We get the noir-ish vibe that he has no other sense of what other life he might lead, apart from spying. Its what he knows best; the only thing he's suited for. At the same time--in the first novel--we do see that Quiller harbors an especial hatred for Nazis; he considers them targets of his particular interest and worthy of his pursuit wherever they may re-appear.
And as far as that is concerned, 'The Quiller Memorandum' is actually one of the finest stand-alone tales of neo-Nazism you can ask for; I would say its even *definitive* for this sub-genre. The strength of Hall's peculiar vision lent itself to a damn fine 1967 film starring Alec Guinness, Max Von Sydow, Sente Berger, and George Segal (titular role); and a screenplay by Harold Pinter. That is certainly top talent, and the flick (though not a milestone) is one of the most evocative films featuring a re-built but uneasy, post-war Berlin.
In general, Hall writes with both poise and grit in equal doses; a touch of 'spy vs spy' surreality, as well as a very noticeable atavism. Initially, it seemed as if Hall's quirky formula might bring him a lot more renown. He's written a string of later Quillers set in the Mid-east and southeast Asia and they feature a variety of flairful enemy organizations and exotic titles like, 'The Kobra Manifesto'. In spite of this, he's always remained a dark horse doing his own thing. Quiller is so subtle that it just won't lend itself to cinema more than once (Hall had other success with 'The Flight of the Phoenix')
Still, the genre is very lucky to have Adam Hall; and all of his works deserve probing--if for nothing else other than his insistence on breaking convention.