Tabitha of the title, 30, unfashionably fleshy, bored with her job in advertising and her sexless social life, meets suave, moody George at a dull Manhattan party. ""What is your blood type,"" George murmurs. George, you see, is a vampire (""I have a drinking problem""), but a Reformed vampire who now only takes blood from volunteers, via transfusions (""We do not, as you put it, lunch off other folks' necks any longer""). George is also 450 years old (""Heidelberg, class of 1547""), but he's just the right age for hard-up Tabitha--great in bed when he's had enough blood, impotent when the donor situation is tight. Anyway, all is positively Transylvanian till Tabitha meets George's imperious mother and, worse yet, his unReformed daughter Nicola, an evil bat-ette with lesbian tendencies. Tabitha fends off Nicola's advances by driving a stake through her heart and soon becomes more and more involved in the vampire subculture--doing PR for VAMP (the Reformed association), helping George to do battle against the hideously unreformed VIAND (Vampires International Association for Natural Diet). Unfortunately, first-novelist Linssen also becomes more and more involved, comic-book-style, leaning on a one-joke premise and a precariously balanced tone (narrator Tabitha is a strange blend of smart, funny, sweet, mean, and vulgar) till they creak like a vampire's coffin lid. With those hilarious getting-to-know-you opening chapters and the amusing advertising-biz vignettes, this is a trendy vampire vaudeville that starts out bloody marvelous but soon becomes a pain in the neck.