Ring

First half of the book is pure gold in an epic scale but I somehow did not like when the handwavium Extra Super FTL hyperdrive appeared, it wasn't that bad to compromise the whole book but I was not expecting that at all. Probably it made sense in some way for the plot but It also made the universe looks like a small city and it sort of broke that sense of wonder you got when you reading about the Ring, super strings, etc.

Apart from that, it could be a full 5 star book.

This is the final book in Baxter's Zelee Sequence but was recommended to me as a worthwhile stand alone book.

As the sun approaches heat death Earth's scientists work out that it's happening much too soon and something must be happening to it. The Zelee series deals with alien wars etc and space travelers also work out that other stars are also degenerating too quickly.

By sending a probe into the sun they find the problem and realise that it's non-repairable and it looks like the whole galaxy is threatened by the same thing.

As the book approaches the end they work out that the aliens with whom they were at war for so long are really the solution to a galaxy wide problem.