Death in a White Tie by Ngaio Marsh

The Social Event of the Season Has Death on Its Guest ListNo one is more popular on London's champagne-and-caviar that charming Lord Gospell. However, on the morning after the year's most glittering ball, someone finds a reason to asphyxiate "Bunchy" Gospell in a taxi headed across town. Scotland Yard's Inspector Roderick Alleyn is called in to find out who killed his old friend, and to cleverly unwind a tangle of murky secrets that began far from the ballroom floor.