Sick young nanny Ida stumbles into the Berlin Charité hospital. Dr. Robert Koch's work on a tuberculosis cure attracts two physicians and an actress.
Spinola repays Behring for saving a life. Ida is urged to pursue an ambitious dream. Koch receives two visitors: a Tokyo doctor and the new emperor.
Koch reveals big news at the congress while Ehrlich struggles to find a doctor to deliver his wife's breech baby. Tischendorf and Ida's romance blooms.
Nurse Therese falls ill. Koch tests tuberculin on humans, starting with himself. Behring reaches a breakthrough in his work on a diphtheria cure.
Despite worrying results, demand for tuberculin overwhelms the Charité. Behring's diphtheria cure is put to the test. Ida meets Tischendorf's father.
Koch fails in one aspect of his life, but succeeds in another. Ehrlich faces a betrayal and increasing anti-Semitism. Ida rethinks her future plans.