What happens when you put time travel, magic, quantum physics, witches, a top secret military operation, alternate timelines, Vikings, a family of shadowy bankers, and government bureaucracy in one book? 
 As you might expect, things get complicated. 
 The story begins with the written account of Melsianda Stokes, a woman from our present who has become stranded in London during 1851. Mel tells us how she's an expert in ancient languages who was stuck in a dead end academic career until she is recruited by military officer Tristan Lyons to take part in a top secret effort translating old documents that make repeated references to magic being done by witches. Mel learns that magic was indeed once real, but that it ceased working in the mid-19th century. Now Tristan is leading the government's effort to bring it back. 
 Mel and Tristan are able to determine what what caused the death of magic, and with the help of a physicist and a very old witch are able to get it working in a very limited fashion. The government demands an immediate practical application to justify the taxpayer expense and using magic to send people back in time to alter events in a way beneficial to the US meets that criteria. However, changing the past turns out to be harder than everyone thought with multiple trips required to make the revisions in several timelines, and causing a paradox has immediate and dire consequences. Soon Mel and Tristan are part of a growing covert department that sends operatives to the past to recruit a network of witches and perform complex missions to make subtle changes, and they find themselves working for infuriating bureaucrats who think they can control everything with PowerPoint presentations and policy memos. 
 That's a very boiled down summary which is what you have to do when reviewing a Neal Stephenson novel because as always there's layer upon layer that you could write essays about. The explanation as to why magic stopped working alone gets into a whole Schrodinger's cat thing about how observation collapses quantum wave functions which is then tied into the rise of technology like cameras. Throw in the usual Stephenson digressions like an explanation of the sexual harassment policy related to issues like wearing codpieces, and you get one of his typical kitten squishers. 
 Stephenson isn't flying solo on this one, and although I haven't read co-author Nicole Galland I could sense that this was a bit more reined in and scaled down from his usual thing. Still, you can see stray bits from other works, and one of the big sci-fi aspects seem drawn directly from one of his other books. Which means that if you've tried Stephenson and get irritated with his quirks then you're probably not going to like this. Usually I love a big fat Stephenson novel for its tangents and offbeat nature, but I found myself tapping my toe with impatience a bit during this one. 
 The second act of this book is mainly concerned with the 'rise of D.O.D.O' part of it, and it's told in a series of emails and policy directives which gives us the picture of how a government agency dedicated to time travel would take shape. I'm usually interested in things about how big projects come together and this also lays the groundwork for 'the fall' piece by showing the development of David Simon Syndrome in the way that any large institution will almost inevitably become about projecting the image of competence rather than risk failure by doing the job it was created for in the first place. In this case the narrow vision and arrogance of those in charge also leaves them vulnerable to threats from within. 
 I get what the authors were going for there, and there's also some good humor laced throughout that part. Yet it just seems to go on for too long, particularly since we know big trouble is brewing because of Mel being stuck in the past. 
 Secondly, for all the explanation and set-up for how the time travel and magic stuff works we never really know WHY it's being done in the first place. There's some mention about the government having indications that others are time traveling and changing things so that would be motivation yet we never get enough detail on that. Plus, no one stops to question whether they should be doing this at all which seems like a glaring oversight. Even when they see first hand the catastrophic results when too big of a change happens they don't hesitate for a second. With poorly defined motivations this seems especially foolhardy. 
 It also seems as if the schemes ignore common sense and get ridiculously complex. For example, the first mission is for Mel to travel back to Puritan controlled Boston and obtain a copy of a book which will be incredibly rare in the future. This is supposed to be proof of concept as well as a fundraising expedition. Fair enough. Since the time travelers can take nothing forward or back with them Mel has to get the book sealed up tight and buried near a rock that still exists in the present. She also has to do this multiple times to force the change through the various time strands to the one they're in. 
 A problem occurs when her strands undergo a shift that has a new factory built on the spot in the past so that she can't bury the book in the location they originally pick. So they start a second campaign which involves Tristan going back to London to shift the investor from building that factory, and again, he has to do this repeatedly to get the change to stick in their timeline. 
 Sooooo....Why not just come up with another location for Mel to bury the book rather than go through the effort of a second mission that requires trips to the past? It's not even discussed that I remember, and it seems like a much simpler solution to the problem. 
 That's kind of the issue overall with this one for me. While it had a lot of stuff I loved (view spoiler)[like a Viking raid on a Wal-Mart (hide spoiler)] and a lot of deep thought was put into the concept it seems like the obvious was often overlooked. I also wasn't crazy about the ending that seems to be more sequel set-up than resolution. 
 Generally I liked it, but it wasn't the usual home run of a book I've come to expect from Stephenson. More like a solid double.