I can't decide if this would have worked better (for me) as a short story, or a full length book. If it was longer, it could have expanded on it's ideas. If it had been shorter, it wouldn't have felt so repetetive.

There is some good ideas here, but they deserve better than being hand waved away. How do Red and Blue target their letters to each other across strands of time? If there are certain contested junctures in time, shouldn't they be swarmed with agents, and multiple aspects of the same agents? If the protagonists are just cogs in two massive opposing machines battling for supremacy over all time - why does it seems like they are the only two operators in the field?

I'm not saying this is a bad book, there is a lot good writing here. But it didn't work for me. Two highly subjective stars. (I'm going to hold of actually rating as there are so few reviews here yet)