A Wreath for Rivera (AKA Swing, Brother, Swing)
Ngaio Marsh Audio Book

The music rose to a climax. Lord Pastern aimed his revolver and fired. The figure in the spotlight fell and what had been intended as a coup-de-théâtre had become murder...

Could Inspector Alleyn believe that the eccentric peer had let the hatred of his future son-in-law go too far? Or would the tangle of jealousies and blackmail among the party guests reveal another murderer?