Plague is an infectious disease of animals and humans caused by bacteria, Yersinia pestis. Modern antibiotics are effective against plague, but if an infected person is not treated promptly the disease is likely to cause illness or death. The purpose of this study is to evaluate at the safety, immunogenicity (bodily defense reaction), and tolerability of a new research vaccine. Up to 48 people will be enrolled in this study at the Center for Vaccine Development at Saint Louis University. Four groups of 12 volunteers will be given vaccine or placebo (inactive substance) one group at a time starting with the lowest dose working up to the highest dose. Shots will be given in the arm 2 times separated by 28 days. Study procedures include: physical exam, blood samples, and recording temperature and side effects in a memory aid. Participants will be involved in study related procedures for about 13 months.