Two men, known in medical journals as the Berlin Patients, revealed answers to a functional cure for HIV. Their cures came twelve years apart, the first in 1996 and the second in 2008. Each received his own very different treatment in Berlin, Germany, and each result spurred a new field of investigation, fueling innovative lines of research and sparking hope for the thirty-four million people currently infected with HIV. For the first time, Nathalia Holt, who has participated in some of the most fruitful research in the field, tells the story of how we came to arrive at this astounding and controversial turning point.