"The wife killed my mom so my revenge was to torture and kill random people".
"Hey assassin, I an underling (but actually I'm the secret true boss), order you to kill the man who you think is the boss" -Imagine if the old man were to just lie to the assassin "Nah I'm the boss, kill him".
This twist wasn't really necessary, the old man being the mastermind was a little better and way less convoluted.