Death's Angel

Summary
From the back cover: Death stalks the corridors of the Enterprise

When Captain Kirk and Mr. Spock barely survived the mission to Delta Gamma Four, the deadly planet whose beautiful blue flowers destroy the mind and ravage the soul, Chief Medical Officer McCoy felt something was dangerously wrong -- just how wrong, he didn't realize. For when the Enterprise takes on the alien members of a sensitive Federation diplomatic mission, the ambassadors are murdered one by one. The angel of death is visiting the Ambassadors.