Vienna, 1913. Psychoanalysis? Check. Looming war? Check. Pastiche imagist poetry? Check. The early stirrings of logical positivism among the first Vienna Circle? Perhaps subliminally, but it would be hard to work that explicitly into a polished middlebrow literary yarn. Otherwise, William Boyd has been nothing if not assiduous in ticking the boxes implied by his historical setting.

Boyd's previous book, Ordinary Thunderstorms, opened by casting the reader as bystander, pointing out an anonymous young man in the street who turns out to be the hero. Boyd begins Waiting for Sunrise with the same trick, inviting you to notice a well-dressed young Englishman, Lysander Rief. He is an actor on the London stage, with "fine straight hair", come to Vienna to seek a talking cure for his inability to orgasm. A kindly Dr Bensimon teaches him to rewrite his own past, and soon Lysander is orgasming all over the place. (One in the eye for Dr Freud, who is seen pooh-poohing Bensimon's theories in a café.)

Lysander has not chosen his new orgasm-facilitator wisely, however: she soon has him arrested on trumped-up charges, and he has to escape Vienna. ("Fucking consequences again," he thinks much later, though I was left unsure whether the possible pun is deliberate or era-appropriate.) Luckily, escaping Vienna proves not too difficult, as Lysander turns out to be a master of disguise. His exploit intrigues a couple of mysterious Englishmen, so Lysander is invited to do a spot of spying when the war starts. First a quick (not to say touristic) trip to the front line in France, then a dab of interrogation, then a holing-up in dingy London offices, on the paper trail of a mole in the military bureaucracy who is passing secrets to the enemy.

Cross Arthur Schnitzler's Dream Story with Sebastian Faulks's Birdsong and John le Carré's Tinker Tailor Soldier Spy, and you might be considered impressively ambitious. What Boyd has made is not so much a hybrid as a series: first, sex in Vienna; next, war in the trenches; finally, counter-espionage in London. Despite efforts to tie them together by means of recurring characters, the parts do not feel interdependent, and none is developed enough to be compelling on its own.

The language doesn't help. What ought to be spectacular set pieces (Lysander crossing no man's land; a Zeppelin attack on London) are hurried along in a flat, outline-ish prose: "[He] looked up just in time to see a window embrasure topple outwards and drag down the half wall beneath it." Perhaps this is aiming for pace and muscle, but the writing is never as rhythmically energising as it is in a good thriller, and there is little in the way of sensuous detail. It reads instead like functional description in a film script, except without the typographical excitement of capitalised PEOPLE and THINGS. Many sentences could have done with extra care: early on, Lysander is seen "staring at a flowerbed in a fearful quandary", which is an unwise place to put a flowerbed.

This is not to say that the novel lacks pleasing craft. While investigating his mole, Lysander pictures memorably the logistical operations of a continental war as black smoke converging on a bonfire, rather than drifting from it. On the same page: "Two women typists faced each other typing, as if duelling, somehow." (Though arguably that "somehow" is effect-diluting.) There is a fine, moody interlude in Geneva, where  in the novel's best scene  Lysander learns he is, after all, the sort of man who can torture another. Meanwhile, Lysander's gay uncle Hamo, a former major and "not particularly famous explorer", is a splendidly gruff and sympathetic creation, of whom one always wants more when he is hustled offstage, too often in favour of Lysander's vampish mother.

In the closing pages, Lysander reflects on his experience: "I was provided with the chance to see the mighty industrial technologies of the 20th-century war machine both at its massive, bureaucratic source and at its narrow, vulnerable human target." It sounds like a sexily sellable one-line proposal for a sweeping first world war fiction; but this curiously unexciting novel hasn't delivered on the pitch.

Freud and Jung in the David Cronenberg film A Dangerous Method; the 150th anniversary of Klimt; and (God help us) the first world war as depicted in Downton Abbey: all that has been missing in this orgy of period nostalgia was a new Viennese eve-of-war novel. In Waiting for Sunrise, William Boyd has come up with it.

At least it begins in Vienna, before becoming very British, just as it is part psychological teaser and part spy novel. Some critics have found the switches of tone and location disorientating, but then Boyd is an unashamedly cosmopolitan writer, and the better for it.

Still, the discontinuities can puzzle. It is with some surprise that we witness our well-born, somewhat effete young actor hero mutate into an ingenious and ruthless spy hunter, but then the author has a cunning excuse. This and every other extravagant turn of events in the book can be justified in terms of the theory of "parallelism", dreamed up by the Viennese analyst our hero travels to Austria to consult (not Freud, though in a nod back to Boyd's Any Human Heart, the great man puts in an appearance, in order to disapprove of the theory).

Based on Bergson's la fonction fabulatrice  the capacity for make-believe that lends colour and meaning to our existence  the idea is that to make life livable the individual puts flesh on the gaunt bones of an alien and indifferent world by dint of his or her imaginative powers. In what in the end turns into a sophisticated whodunnit, the author freely deploys his own fonction fabulatrice here.

The problem of conjuring a Viennese backdrop  if you don't, the critics will get you for it; if you do, it'll have to be avant-garde artists and opera and prewar decadence, served in a rich sauce of sexual neurosis  is resolved by the latter method. Boyd would appear to know his Vienna well and in the insistent clutter of description  clothes, drinks, meals, interiors, street scenes, nothing escapes  there is a faint echo of Joseph Roth in The Radetzky March, the great eve-of-disaster Austrian novel in which the accumulation of period detail helps create an atmosphere so stifling the thunder has to strike.

The transitions from sexual intrigue to family drama to trench warfare and finally a slightly dated fin de siècle Holmesian espionage romp maintain the momentum. It would have made more sense if the entire plot had taken place in Vienna, instead of shifting to London, but that would have deprived us of Boyd's successful fabulation of the Whitehall military-bureaucratic machine and espionage establishment, in which "C", its newly created boss, has a walk-on part.

Before long, we sense that Boyd is not entirely master of his material, in the sense that the meandering plot seems to have taken charge of the author, rather than vice versa. Stylistically, this shows in a couple of indolent anachronisms (did we say "up for it" in 1914? We didn't in 1970) and an occasional insouciance in the writing  "Once again I wonder what machinations have been going on behind the scenes"  though perhaps we are meant to read this as spoof Sherlock Holmes.

The whole thing can be seen as manufactured, but then it is done by a craftsman's hands and with polish. I was about to add "and after all, contrivance is part of the genre", but then I'm not quite sure what the genre here is. Is there some message I'm missing? I doubt it, but much it matters. Here and there, we encounter weighty insinuations appropriate to the times, such as the notion that an underground "river of sex" flows through Vienna (and  who would have thought it?  London too), but the best way to read the book is to avoid over-analysis and turn the page. On a more homely level, amid the violence, skulduggery and frantic sex, Boyd has a knack for inserting amiable human touches, such as the hero's warm relations with his gay uncle.

What are we to make of it all? Not too much or too little. It would be mean-spirited to focus on structural or stylistic defects to the exclusion of the enjoyments of a story of no great depth or pretensions but good on atmospherics, and which, after a slowish start, will deliver the requisite satisfactions to all generations of readers.