Germ Slayer Essential Oil Blend 1/3 fl oz. Germ Slayer is a blend of clove, lemon, cinnamon, eucalyptus, and rosemary. The history of this essential oil blend was derived from the story of four thieves who robbed people during the bubonic plague in 14th-century Europe. During this time, the four thieves went from house to house robbing those who had succumbed to the illness. After their capture, the thieves claimed that they wore masks combination of herbs, spices, and essential oils to protect them from harm. The popular blend is still used today to help support immune systems and kill bacteria and viruses.