The story of this manga is about how the main character, a super neurosurgeon, once saved a boy, and the boy turned out to be a maniac, a monster. When the doctor became suspected of various murders and he finds out who he saved, he sets off in pursuit of this boy, believing that he is guilty because he saved him. He was going to kill him. That's the short version, but there's a lot more to it.
Spoiler:
In the end, he still couldn't shoot the now-grown guy, and when the guy was shot, he saved his life a second time. It was quite unexpected for me, but interestingly done.