The End of Eternity by Isaac Asimov (1978, Paperback)

The story opens in the strange all-male world of the time-travelling Eternals, with its unfamiliar ranks and hierarchies. It has points in common with both professional science as it was in the 1950s and with the military - designations like the 482nd Century remind one of military terminology. But it is also a thing in itself.

The top rank are known as Computers — true to the original meaning, someone who performed complex calculations, with or without artificial aids. In this case they have access to a 'Computaplex' or 'Computing machines'. Asimov was rather ahead of his time in recognising the limits of such devices - they depend on the assumptions fed to them. There is also the small unavoidable element of uncertainty which cannot be removed: this was well before chaos theory proved that any system must suffer such limits.

The psychology of the protagonist Harlan and the other Eternals is interesting. Not a vast amount of introspection, but an odd view of the world, in time rather than space, that emerges by conversations and conflicts among people who see it as normal. Women are a confusing element, prized but generally unavailable. One particular woman is pivotal to the plot, of course, and it is a strange kind of love-story as well as a mystery and thriller
I love this book i consider it one of his best works