Although Vivien Thomas (Mos Def), a black man in the 1930s, is originally hired as a janitor, he proves himself adept at assisting the Blue Baby doctor, Alfred Blalock (Alan Rickman), with his medical research. When Blalock insists that Thomas follow him to Johns Hopkins University, they must find a way to skirt a racist system to continue their study of infant heart disease. Thomas is indispensable to Blalock's progress, but Blalock is the only one who is allowed to receive the acclaim.