It's Valentine's Day in the ER. However it proves to be a tough day when Chen and Malucci clash over the treatment of a patient, the parents of two young children die in a car accident, Lucy and Carter treat a law student who she believes may have mental problems, Romano and Elizabeth operate... on his dog, and Abby learns that not all ER cases have happy endings when she treats a dying elderly woman. Mark and Elizabeth go out on a double date with her mother and his father. At the end of the day, the staff party, unaware that Carter and Lucy have both been stabbed by Lucy's patient.