Recursion

The story revolves around a memory device that can bring people back in time to a memory that they then can change -- but it changes everyone else's memories, and they can then remember those timelines as well. Mindbending fun.

Interesting concepts about memory and time and how screwing around with both/either can have catastrophic consequences. I didn't think the world building or the characters were very well-developed, but it did make for an entertaining story. 

The book starts out slow with a few cliches. I wasn't impressed. But that's all part of the plan; I'm glad I didn't give up.

The conceit of the story, recursion, is investigated completely and exhaustively to the point where you are completely exhausted and thrilled. Beautiful ending (It shouldn't be an epilogue though! Too necessary.).

This was a brilliant work of science-fiction. I've been totally engulfed into the story, between Helena and Barry and their race to save the world of a terrible invention. But also deeply questioned about the nature of our memories, sense, and apprehension of time and its complexity. This was really well written and I must admit that I had a big problem letting go off the book for the last half !