An unnamed time-travelling dystopian-future dude has to stop someone (himself?) from killing him a year from now at the birthday party he throws himself every year. But if he dies next year, why are there still older versions of himself at the party - shouldn't they never exist?
Sometimes I suspect I'm not smart enough for science fiction; I was continually confused and a little delirious about who, what and which version of the narrator was bending which paradox. The narrator's habit of giving differently aged versions of himself nicknames based on some notable characteristic or experience (The Drunk, Seventy, Screwdriver, and The Inventor) aid the unpuzzling - but also make it easy to forget it's all just future and past versions of the same guy.
The reason I persevered is the storyline that takes place from the party - about a woman he meets the night of the murder, then backtracks six months in time to attempt to steer her away from the party. That six-month story was way more interesting to me - and by the time we caught up to the party again, I simply had to finish to find out what happened.
This book was a tough row to hoe for me, but I suspect there are time-paradox fans who will find it much more though-provoking and engrossing than I.