Scythe -Neal shusterman

thou shalt kill 

what if death was the only thing left to control? 

In a perfect world, the only way to die is to be gleaned by a professional scythe. When Citra and Rowan are chosen to be apprentice scythes, they know they have no option but to learn the art of killing. However, the terrifying responsibility of choosing their victims is just the start.

Corruption is the order of the day and Citra and Rowan need to stick together to fight it.

Then they are told that one of them will have to glean the other...