While sorting through books for an upcoming move, I came upon my husband's cache of Agatha Christie mysteries and have been devouring them all summer. My favorites were written during the 1920's and 1930s, a period that roughly coincides with the heyday of the cocktail. While Christie's characters aren't heavy drinkers, they do like their gin: pink gin, double gin, gin fizz. In The Murder at the Vicarage, the fussy Mrs. Ridley describes her reaction to hearing a gun shot: "Clara had to bring me a glass of damson gin!" And here's Tony Marston, pausing on his way to an island retreat in And Then There Were None: "Heaps of time! . . . He'd have a gin and ginger beer. Fizzing hot day!" Given his fate, poor Mr. Marston should have stayed for a second and missed his ferry to Indian Island.