Star Trek Death's Angel (1981) Paperback Book

When Captain Kirk and Mr. Spock barely survived the mission to Delta Gamma Four, the deadly planet who 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 missions, the ambassadors are murdered one by one. The angel of death is visiting the Ambassadors.