Carol overcomes a few initial jitters and heads back to work in the ER. Mark treats a woman who is a victim of domestic violence. Susan clashes with Kayson on a cardiac case. Carol learns a valuable lesson from a leukemia patient. Carter has a tough time keeping up with Benton, and cares for an Alzheimer's patient with a melodious voice. Doug struggles with his feelings for Carol. The staff celebrates Carol's return with a surprise welcome back party.