In my experience, this is the best book about martinis: The Hour by Bernard DeVoto
A now unjustly-neglected essayist and critic, DeVoto published The Hour: A Cocktail Manifesto in 1951. It has been reissued recently. It is full of wisdom and clarity. Here’s a favorite, as he contemplates the martini hour: “This is the violet hour, the hour of hush and wonder, when the affections glow again and valor is reborn, when the shadows deepen magically along the edge of the forest and we believe that, if we watch carefully, at any moment we may see the unicorn.”
Of course, as he points out, the virtue is that you may see the unicorn. If you actually see the unicorn, that’s another issue entirely.