It's probably appropriate that the inevitable quote on the front cover of 'Invisible Sun', the last in a trilogy that continues the stories of multiple timelines introduced in an earlier trilogy that was originally published as a six book series but then compressed, is not by an author but an economist. Paul Krugman won the Nobel Prize in economics and if you wonder why he might have anything to say that a potential reader might want to listen to, then this may not be for you.

The first book, 'Empire Games', read like both a science fiction exploration of a multiverse and the sort of Cold War spy novel that might have been written if the two sides weren't a pair of nations on the same planet but a pair of global superpowers on parallel worlds who could visit each other. That only escalated in the second book, 'Dark State', which was so detailed that it often felt like an alternate history textbook that we might study in college. Fortunately, this third book, wraps up a complex set of plot strands without following suit. Yes, it's incredibly detailed, worldbuilding at its most anal, but it's also a much more accessible science fiction spy romp than the middle book.

It would be nigh on impossible to sum up everything here and you really, really, really don't want to start here. If you're interested in a story with worldbuilding this detailed, then pick up all three books and read them in order. In fact, don't do that. Pick up the three/six books before it, that are collectively known in either incarnation as the 'Merchant Princes' series, read those first (which I haven't), then and only then, dive into this trilogy. It ought to grow more naturally for you in that order.

However, I'll give it a shot. There is a multiverse with an infinite number of parallel Earths, but we care about four timelines, numbered one to four for our convenience. The 'Merchant Princes' are in timeline one, but they decided to detonate a nuclear bomb in the White House in timeline two, which diverged away from us at that point. It shouldn't surprise that the Americans retaliated, so timeline one is now radioactive fallout. However, some people survived by worldwalking over to timeline three.

The Americans in timeline two believe those worldwalkers are terrorists, so are spying on them, but they're not really. They, however, realise that they have to bootstrap timeline three as fast as they can to a technological level that will be able to cope with timeline two, when it decides to do something about them. Timeline four is uninhabited but for a military base built by timeline two, which has now been invaded by alien robots, which ought to shake everything up.

The cast of characters is immense but the ones we should be focusing on are naturally in timelines two and three.

The key players in timeline three are mostly the worldwalkers from timeline one. They're resident in the North American Commonwealth, a democracy formed after a revolution to free them from the yoke of the British Empire, which is run from exile from North America because France are the previous global superpower and they've successfully invaded the UK. However, the First Man, the leader since that revolution, has died and the American military from timeline two are dabbling in their politics in an attempt to subvert their stability and weaken them, which they manage by prompting a coup by Commonwealth loyalists to prevent a coup by Commonwealth Loyalists that isn't happening. Oh, what a tangled web.

I say mostly, because the MacGuffin of the piece, in a variety of ways, is Elizabeth Hanover, heir to the British throne who has been promised to the Dauphin in marriage. She doesn't want to know, so is preparing to defect to the Commonwealth, but she's getting there via Berlin in timeline two. However, her timeline three contacts have been captured, which means that the race is now on to find her, with both the Americans from timeline two and a group of East German sleeper agents, from timeline two but working for timeline three, attempting to reach her first. This is the reason why this reads so much more energetically than the second book, because this is textbook thriller, rather than just textbook.

And I'll quit with the synopsis, because I'm scratching the surface and I won't go on forever. These are deep books that require us to pay attention—if we don't, we're going to get quickly lost—but they are surprisingly accessible, given how much information we have to process. It's telling that the lead character arguably changes in each volume of the trilogy, because our focus changes. In so many instances, important characters lose their importance once they reach a particular point, while supporting characters gain importance as the complex plot tags them in and sets them on a particular task.

From the standpoint of worldbuilding, this is incredible stuff but it's so detailed that you have to care or you're going to give up quickly, especially during the middle book. I struggled through the first, not having read the 'Merchant Princes' books but found it easier going after that. In fact, I read this volume a lot later than I expected, but I picked everything back up as if there was no gap in my reading and I'd just rolled from book two to book three. The only negative I'd throw out with this angle is that what goes down in timeline four would seem to have far more ramifications than are resolved here. This is supposed to be "the final tale of the Merchant Princes Universe" but I'd be surprised if these alien robots don't show up in future works. I'm not sure Stross can resist.

Regardless how well he handles the worldbuilding, which is a science fiction angle, I'd say that this works better as a Cold War spy thriller. It's the adventure side that enthralled me here, partly in a grand game of politics but mostly in the smaller stories of individual missions. There's a tension in these scenes that's delightfully palpable and only grew with the escalation of stakes. That they're also old school vs. new school, Cold War tradecraft vs. Echelon level surveillance, only adds to that tension. Elizabeth Hanover is such a fantastic MacGuffin too, a fish out of water not only from the standpoint of intrigue but as a woman who knows her Berlin trying to navigate a different one in spite of wild differences in the culture and level of technology.

She's a personification of one of the key concepts that Stross used to build this trilogy, namely the development trap. This has to do with the complications that manifest when trying to escalate the development of a civilisation to the level of another. There have been instances of that working to amazing degrees in our world, especially Japan, which moved from feudal society to technological leader in a surprisingly short time. However, there are far more instances of it failing dismally but the reasons why it works here but not there are far from clear. Stross has fun with that and we see it the most when looking at Elizabeth Hanover's cultural shellshock while wandering in the Berlin of timeline two.

Now that this immensely detailed trilogy is done, which I've enjoyed in ways I didn't expect after a little shellshock of my own reading 'Empire Games', I ought to dive back into Stross's Laundry Files because they're more straightforward, more accessible and, from my experience with just one of them, simply more fun. ~~ Hal C F Astell

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