In the novel's somewhat dystopian world, human personalities can be stored digitally and downloaded into new bodies, called sleeves. Most people have cortical stacks in their spinal columns that store their memories. If their body dies, their stack can be stored indefinitely. Catholics have arranged that they will not be resleeved as they believe that the soul goes to Heaven when they die, and so would not pass on to the new sleeve. This makes Catholics targets for murder, since killers know their victim will not be resleeved to testify.
