What is the climax of The Secret Life of Walter Mitty?
The climax to this story isn't easily identified. I've read commentaries on this story that say the story doesn't have a climax. To some extent, that does make sense—the story weaves through Mitty's reality and fantasies so seamlessly and quickly that it doesn't follow a typical plot structure. However, the story does have a conflict that runs throughout the story. This is the conflict and tension that exists between Mitty and his wife. She treats him like he's incapable of thinking and doing things for himself. Consequently, Mitty loses himself inside of his fantasies, envisioning himself as a brave, take charge-kind of guy. Mitty wishes that he was more like his fantasy personas, and readers get to see a little bit of that come through in his reality. Near the end of the story, Mitty's wife is reprimanding him once again; however, this time he stands up to her (if only for a brief moment).
“Couldn’t you have put them on in the store?”
“I was thinking,” said Walter Mitty. “Does it ever occur to you that I am sometimes thinking?”
She looked at him.
“I’m going to take your temperature when I get you home,” she said.
I believe that this brief sequence could be viewed as the story's climax, because it is the moment when Mitty meets his main conflict/antagonist head on. Readers get the impression that his wife is stunned at his words. She's so stunned that she believes that something must be wrong with his health for him to act so out of character.
The climax of this wonderful little story is when Walter Mitty faces the firing squad. However, what exactly does that mean? It's not fully clear due to the nature of Thurber's story. To be specific, Mitty's fantasy life is much richer than his dull, limited, and henpecked daily existence. He regularly escapes into fantasy, and that's what he does at the end when his wife takes too long.
In doing so, he essentially commits himself to living in fantasy, rather than reality. Now, there is some ambiguity as to what that will mean here. Sometimes there's a close connection between fantasy and reality (the sound of one engine becomes the sound of another), but it's not fully clear how close it is here. It's possible that the firing squad is all in his head—but it's also possible that this is Mitty's wife "firing" questions and accusations at him.