This Is How You Lose the Time War - Amal El-Mohtar, Max Gladstone

In the ashes of a dying world, Red finds a letter marked "Burn before reading."

So begins an unlikely correspondence between two rival agents in a war that stretches through the vast reaches of time and space.

Red belongs to the Agency, a post-singularity technotopia. Blue belongs to Garden, a single vast consciousness embedded in all organic matter. Their pasts are bloody and their futures mutually exclusive. They have nothing in common---save that they're the best, and they're alone.

Now what began as a battlefield boast grows into a dangerous game, one both Red and Blue are determined to win. Because winning's that you do in war. Isn't it?

A tour de force collaboration from two powerhouse writers that spans the whole of time and space.