In a unique episode, the path of a butterfly is the deciding factor in the fate of the young doctors. A butterfly landing on a woman's breast sets off a chain of events ultimately resulting in the death of J.D. and Turk's patient, leaving them to wonder what they could have done to change the outcome of their day. Taking a step back in time, the butterfly takes a slightly different path, landing instead on a man's chest and setting in motion an alternate chain of events that leads our characters down a very different path. Will this be enough to change the fate of their patients?