Walter Mitty is a quiet, young man who is constantly caught up in his vivid daydreams. He works as a proofreader for a Pierce Publishing Company, still lives with his mother, and is engaged to a young woman named Gertrude. But it's clear that Walter enjoys his daydreams more than he does his real life. One day he meets up with a young woman named Rosalind Van Horn, a woman who looks just like the woman that keeps appearing in his daydreams. Rosalind is in danger and, seeing that Walter appears to be a nice young man, seeks out his assistance.
This particular scene finds Walter and Rosalind riding in a cab. Rosalind is currently escorting an elderly gentleman named Carl, who is holding valuable information. Walter, having ridden with Rosalind earlier, had to track her down after realizing that he had left his briefcase in the cab. Now that he has been reunited with his briefcase, he's taking the cab with Rosalind and the gentleman in order to return to work.
It's a short scene but amusing scene. The part I find especially amusing, which makes me chuckle every time, is that Walter seems more concerned about the fact that he's going to be late for work, than the fact that an elderly gentleman has just been murdered by some mysterious person. Walter has lived such a sheltered, inexperienced life, that you just can't help but chuckle.