Burn before reading.
The West Coast branch of Binary System Podcast usually gets dibs on any new Gladstone book. However, Elizabeth’s in the process of reviewing The Empress of Forever this time, so his latest one is mine, all mine, Mwaa haa haa haa!
Ahem. Anyway, Max Gladstone and the Hugo Award-winning author Amal El-Mohtar have teamed up to co-write This Is How You Lose the Time War, and I couldn’t find even one instance where one author’s writing overwhelmed the other. The two styles blend seamlessly in this story of two women fighting on opposite sides of a war where both the ultimate weapon and the battlefield itself is time.
The trope of two opposing fighters forming a bond with each other is a familiar one, for good reason. Being the very best sometimes means being set apart from everyone, except the person who’s equally skilled. And both Blue and 
Red are the best that the warring factions of Garden and Agency have created in the long and impossible-to-follow war across time.
The book explains the mechanics of time travel in the most effective way, by not explaining it all. Red and Blue step across time and across alternate timelines like someone jumping from a sidewalk to a mountain stream to a catwalk a hundred stories in the air. The two agents can nudge the flow of history with a careful word here, an undetected assassination there, or a quick nuclear war that turns an entire timeline into radioactive waste.
The fact that this is a time war means it literally never ends. Anything that’s done can be undone; one agent can carefully move an entire army into position, only to have the entire plan fall apart because the other agent went upthread (ie: into the past) and used the Butterfly Effect with a surgeon’s touch to change the whole outcome.
Start a stone rolling so in three centuries you’ll have an avalanche.
The two agents have access to enough impossible technology that they can adjust or even merge time streams using specially-designed chemical time bombs in animals, or trees, or the calcium inside bones. Missing each other by seconds or centuries, the two agents start taunting each other with messages that can only be seen by someone who can read the pattern of atoms in a burnt piece of paper, or the pattern of tea leaves in a porcelain cup that happened to be used as a replacement when another cup cracked at just the right moment.
It’s really only a matter of time before the back-and-forth messages turn into love letters.
And oh my, all of this is just so beautiful. Not just the settings (Garden is an ecological hive-mind paradise filled with poison, Agency is a technological dystopia like something out of an Adam Warren drawing), but the language too. Red and Blue share more and more about themselves and their lives, seeing echos of their primary colors in everything, and blending those into metaphors and endearments (“My Careful Cardinal”, “My Dearest 0000FF”.) Their letters are poetry, the way the letters are delivered is poetry, hidden in seeds and tea and fire, with just enough humor that a reference to opening letters without “destroying the seal” made me smile.
The two learn about how much they have in common (for instance, both of them hate Atlantis, in any form in every time thread), they exchange experiences and hungers and book recommendations, and they gradually discover all the ways it’s possible to love someone that you never meet face to face and who you’re in competition with all the time.
I want to chase you, find you, I want to be eluded and teased and adored; I want to be defeated and victorious – I want you to cut me, sharpen me. I want to drink tea beside you in ten years or a thousand.
It’s beautiful even when the worst happens and the two are suddenly pitted against each other, with the leadership of both factions watching, knowing that failure to kill their target will have the exact same consequences as refusing to try. Knowing that surviving an assassination attempt is as good as executing the assassin. Even that total despair is lyrical.
She makes it ten threads over, a continent away, several centuries up, before she collapses at the foot of an enormous rainbowed wall of water called Mosi-oi-Tunya and does not weep.
This book is utterly lovely, is what I’m saying. It’s the kind of read that I could probably power through in a couple of days, but I deliberately paced it out in tiny delicious chapters over the course of a week to make it really last. The authors managed to dodge the usual time travel pitfall (that is, if you follow the story’s own logic you get to the point where the story couldn’t have happened) by wrapping everything in a satisfying tangle of cause and effect and a fairytale image that was set up almost from the moment the story began.