Where does Mr. Mitty's "secret life" take him? What does he become?
Walter Mitty becomes the most awesome person in the world in each of his "secret life" dreams. Walter Mitty is normal to a fault. He's essentially invisible to the people around him, so he imagines himself as an important, powerful, and central figure in each daydream.
He first imagines himself as a brave Navy pilot flying through a really bad storm. He is the only member of his crew that acts calm and brave.
Walter next imagines himself as a great surgeon that saves the day when an operation takes a turn for the worse.
A third day dream involves Walter on trial for murder. He didn't commit it, but he does admit that he is a good enough pistol shot to have done the murder.
Another daydream places Walter in the cockpit of a fighter plane. He is the last and lone help for the Allies.
Lastly, Walter's imagination places him in front of a firing squad.
In each case, Walter imagines himself as the hero of his own adventure story.