The staff prepares for Valentine's Day. Romano brings his dog into the OR for surgery. The rivalry between Chen and Malucci hurts a patient of theirs. Abby treats a former patient of Carter's and learns that not every story in the ER has a happy ending. Luka must tell two children that both of their parents are dead. David Greene and Isabelle Corday meet and hit it off. Lucy seeks advice from Carter while treating a young law student who may have schizophrenia, but he keeps brushing her off. When he finally gets around to checking on Lucy, he finds her lying on the floor, stabbed in the chest, just after being stabbed himself...