In 1898 Cuba, U.S. troops who have survived the Spanish-American War are now dying by the hundreds from disease -- yellow fever, known as "yellow jack." Major Walter Reed, an Army physician, struggles to find the cause of the infection and to overcome governmental interference. When an answer seems at last possible, Reed decides that the only way to test the theory is to expose his own men to the disease. He cannot order men to undergo the test. Yet finding volunteers seems impossible. Without them, though, yellow jack will perhaps kill millions.