Many-worlds universe, the eponymous Cowboy Angels are elite Company operatives from The Real, a sheaf in which America is unquestioningly the predominant power, and in which it controls the Turing Gates that allow travel between sheaves. Formerly tasked with restoring, by any means necessary, the status of ruined Americas across parallel sheaves, the Cowboy Angels have now been emasculated by the election of Jimmy Carter by a public tired of the endless wars in the sheaves and distrustful of the Company's methods. But some within its ranks view this change as a betrayal, and are ready to act to preserve their idea of America's Manifest Destiny. Adam Stone, a former operative "disgraced" by his whistle-blowing on Company activities, is brought back in from the cold in order to track down an old friend on a killing spree across the sheaves. As his mission proceeds, Stone gradually unfurls a far-reaching conspiracy that aims to tear up Carter's peacenik doctrine and to change all of the histories of all of the Americas across the sheaves.
While bemoaning my last visit to McAuley's bibliography, I remarked that I was reluctant to give up on him because of his past form, especially the fantastic Red Dust. I'm glad that I kept to this as I'm pleased to be able to report that Cowboy Angels finds him in more traditional good form. It's far from having no flaws, but it makes up for these by presenting a rather novel, political take on Everett's audacious solution to the measurement problem. McAuley has a lot of fun inventing plausible alternative "present-days" (actually, the 1980s) that differ because of some 20th century change, including an America ruled by the fascist Bund, many atomically-ruined Americas, and a curious (to the novel's protagonists) sheaf in which Richard Nixon was brought down by an incident in a Washington hotel. By making The Real so clearly not our universe and then presenting a number of alternatives, McAuley also makes the novel something of a spot-our-universe puzzle for the reader. All of which contributes to this being a definite step along the road to recovery for my opinion of McAuley - though, to be sure, both The Quiet War and Gardens of the Sun are more recent novels.
But it's not all good news. While starting strong with an enjoyable first half that frames the multiverse setting, the novel does tend to devolve into a lot of confusing running around and double-crossing in the second half. To the point where this reader lost the plot a bit, and just let it wash over him instead. It's also rather slender on science fiction later on, instead becoming more like a generic thriller. It does keep introducing science fiction elements, including an inexplicably underdeveloped time travelling subplot, but these definitely take a backseat to a series of increasingly tortuous noir-ish switchbacks. As well as the time-travelling subplot, McAuley leaves a number of very obvious points, often directly alluded to, more-or-less completely unexplored. So while there are sheaves in which humans are completely absent and sheaves that are populated by ape-like semi-humans, there's very little about more plausible alternative worlds beloved of writers (e.g. Nazi victory in WW2; Europe destroyed by the Black Death).
And McAuley is also vague about how his multiverse actually works - taking Everett's Many-worlds seriously would imply that any "corrections" to the path a particular universe has taken would merely split that universe into "with" and "without" branches, and that the Cowboy Angels are effectively largely wasting their time. And that's even before one factors in what a human's decision to intervene in a particular way in a particular universe actually means - a conundrum that's probably best avoided by novelists (though Egan makes an excellently full-throated stab at a competing QM interpretation in his novel Quarantine). But, as illustrated by Iain (M.) Banks' recent foray into multiverses, McAuley is not alone in this sort of fudging.
Overall, for all of its flaws, Cowboy Angels is a much more edifying and enjoyable read from McAuley. It's no return to form (and even if it was, he's written worse afterwards!), but it'll more than enough to ensure my continuing loyalty. For now anyway. Writing something with more of the imagination on show in his early novels would be very much appreciated.
In passing, in reading so much about 20th century US politics in Cowboy Angels, I realise that, at times, I know a lot more about what's gone on west of the Atlantic than I do for corresponding periods in my own country. The pre-Thatcher UK political landscape is largely a mystery to me, but I know quite a lot about Roosevelt, LBJ and a certain Milhous. I guess that's fallout from the American Century.