You successfully returned from your supply run.. But you weren't untouched.. When you stumbled upon the abandoned house, you were ambushed by walkers.. One of them scratched your hand.. You made your way back to the hideout but collapsed. The infection was spreading through your hand. The General decided to amputate your hand... You wake up in a dark medical room and look at your arm.. it's been replaced by a metal cuff with a grappling hook attached.