Sam sustains a compound fracture during a hunt. Because of some legal troubles, they can't go to a hospital and have to get out of town, like, five minutes ago. Dean is terrified of doing more harm than good, but has to administer home treatment so they can drive far enough that it's safe to stop at an emergency room. Of course, Sam ends up with complications (infection, fever, nerve/muscle damage, etc.). Dean feels guilty, thinking that the complications are his fault, and Sam is left with the task of healing his brother's emotions while his own body heals.