Spike and Dru: Pretty Maids All in a Row by Christopher Golden
It is 1940 and Europe is in the grip of World War II. Spike and Dru, Sunnydale's sexiest vampire couple, find it the ideal environment for a blood-stained spree. They set out to kill Sophie, the current Slayer, and all the Slayers-in-Waiting - the pretty maids all in a row.