Summarize the last dream of Mitty where he says "Mitty the undefeated, inscrutable to the last." answer with introduction

Walter can only dream of being "undefeated, inscrutable to the last."  Only in his dreams is he strong, courageous and formidable.  On their way home, Walter's wife must make one more stop at the drug store.  There she orders him to wait right there outside the store for her.  She'd "only be a minute." Walter's life has been one nag after another from his wife.  People in society make fun of him.  The ladies at the store, the parking attendant, just people he encounters in every day life laugh at him and find him incapable.  As a man that's hard to accept. So in his dreams, he is the hero.  He always comes out on top.  As his dreams continue through the story, they lead up to the most elaborate dream of all.  He is imagining himself in front of a firing squad, smoking his last cigarette.  If it were real life, this would be his last moment alive, yet in his dream he is calm and confident--right down to the last moment.  So in this last dream he says, "To hell with the handkerchief." Then he takes one last puff on his cigarette and casually yet confidently flicks it to the ground.  He turns and faces a squad that should be terrifying to him.  Yet, he smugly smiles at them showing off his heroic qualities.  This is important because in this dream he is facing death.  He is not afraid.  His "dream-self" will not falter or go down.  He feels invincible.