At a swanky rooftop restaurant in New York, a pair of husband-and-wife sleuths must find out who spiked a woman's drink with murder . . .   There's a stunning view from the top of the Ritz-Plaza Hotel, but it pales in comparison to Lois Winston's beauty. She arrives on the arm of David McIntosh--an agreeable young man who would marry her if she gave him the chance--to take in the scenery, eat a light supper, and forget the busy world below. Lois's first cocktail lifts her spirits, helping her dispel the strange sadness that tugs at her soul. But her second drink isn't so kind. Lois isn't halfway done with her Cuba libre when her cheeks grow hot, her breath becomes short, and she falls dead to the floor.   Solving the case of this terribly fashionable murder falls to New York Police Department's Lt. William Weigand, who tackles the investigation with the help of his friends, Jerry and Pamela North. The effervescent couple will catch the killer between cocktails--unless the poisoner targets their glasses next.   "[An] excellent series." --The New Yorker   "Pam is always amusing."  --The New York Times