Thriller Idea

My thriller idea is about assassins/hitman(or women, or is it the same for both genders?), that has killed so many that he/she feels as if their soul is slowly dieing with each life he/she takes. This will lead the killer to flee from his guild to set up his own life in secret. However due to the guilds beliefs the only escape from their work is death, otherwise their secrets and tricks could be let loose onto the public. This leads the guild to send out their highest killers to take down the protagonist. Plot twists could be that the people told to kill the lead had no idea who they were after, and this could be revealed by one of the protagonists long lost friends with a knife to their throat, only to realise their identity.

Another idea i had (also about assassin/hitman sort of things) is about the protagonist hearing a voice inside of his/her head which plays with the protagonists mind, for example with one of the most powerfulgang leaders in their grasp the spirit inside lets out a highpitched squeal forcing the protagonist to collapse in pain, allowing the target to escape, but helping as in warning of a attack from the left allowing the protagonist to move out of the way and counter the punch. Also the voice can communicate much more clearly through the protagonists dreams, and has slight control of their body. I think i got this idea from a video game Assassins Creed, as this relys ona puppet system giving them complete control of his ancestors, but this will also help to set up a lot of mystery onto who the voice is.

I think i may have thought too much into this... :)