Story about an assassin who travels to a parallel Earth to carry out an assassination

Question

Read this about 7-10 years ago

• Futuristic. Assassin kills people, then has his memory wiped (voluntarily). He moves a few beer bottles in his fridge to keep count of how many people he's killed

• Scientists discover a worm hole, and through that, a parallel Earth

• Assassin is asked to steal a spaceship, investigate the planet, and kill a scientist there

• Some complications occur, and he meets a woman

• Half way through the job, his time expires, and his memory is wiped out, and he forgets the mission and the woman he met. He then tries to kill her, till she tells him of the secret of his beer bottles. He can't remember the mission, but decides to trust her.

• They finally do kill the scientist, I think.

At the end of the book, the assassin finds out

that there are many parallel Earths, and he is from one of them. The main Earth has been killing scientists on the other worlds to keep them backward. The assassin decides to go back to him home planet and destroy the corrupt system

Answer 1

This is Zero World by Jason M. Hough.

This review mentions the beer bottle counting system

This will be the most interesting mission you’ll ever forget.

These words are spoken to assassin Peter Caswell by his handler, Monique Pendleton, as he sets off on the main story arc of ZERO WORLD. Peter is good at his job. At least he thinks he is. He believes he has to be since he continually gets work from his employer, the Archon Corporation. But in this futuristic world, once he completes his mission and eliminates his targets, his memory is wiped. He remembers nothing about what he has done or who he has destroyed. He has secretly devised a count system, employing bottles of beer that he turns so that his re-awoken self knows how many souls he took before the reset, and he recites lines from a Queensryche song to keep himself centered as his memory is erased.