Two boys brought in after a fight at school leads Cleo to discover that one of them has been injecting himself with hormones. Hathaway's obstetrics nurse, Abby Lockhart, joins the ER as a third year medical student on an ER rotation.

Dr. Greene and Corday bond with their parents, Lucy cares for a patient with a psychotic break, and Valentine's Day celebrations in the ER end tragically for one of the students.

Carter and Lucy are discovered and the staff struggles to save them and go on with normal patient care.

Kovac witnesses an accident and saves the young victim's life. Carter slowly recovers from his brutal attack and undergoes excruciating physical therapy. Hathaway helps two sexually active 14-year-old girls.

Even though he suffers from intense pain due to his stabbing injuries, Carter returns to work and prescribes a controversial procedure for a suicidal patient. Greene tries to convince his father to undergo cancer treatment.

Numerous mishaps threaten to mar Corday and Greene's wedding day. As the very pregnant Corday becomes increasingly agitated, the presence of her bickering divorced parents does little to improve her mood. With the intense rain, Greene has a difficult time making it to the church. But, evenutally, he arrives and they joyfully wed.

Dr. Carter, Abby and other staff of the ER are quarantined as the CDC investigate a mysterious, deadly outbreak.