The Last Cup Agatha Christie

These six were seated around a grand, circular dining table in a luxurious nightclub, a table set for seven, with one seat conspicuously empty. A sprig of rosemary was placed before it, in fragrant memory of Rosemary Barton, who had died at that very table, at that very time, last year. None present could ever forget her face, or her remarkable life. But which of them specifically intended to kill her?