Between is the story of a town under siege from a mysterious disease that has wiped out everybody except those 21 years old and under. The series explores the power vacuum that results when a government has quarantined a 10-mile diameter area and left the inhabitants to fend for themselves.
200-year-old Min Se Yeon has managed to conceal her immortality, up until she meets Lee Jung Hoon, a social worker she saves from a traffic accident. Despite her wizened age, Se Yeon is fresh, beautiful and forever in her prime, but with immortality comes a price. Can Se Yeon and Jung Hoon defy time in the name of romance?