The staff react to the arrival of Dr. Dylan West (Rick Schroder), a self-assured, charming surgeon who knows how to push Lu's buttons, having supervised her internship at another hospital. On Dylan's first day, a train derailment floods the ER with patients, including a woman who's seven months pregnant and in critical condition. Meanwhile, Lu is undecided about marrying Jonas. Nestor Carbonell. Agent Norton: D.C. Douglas. Henry Morales: Gonzalo Menendez. Delia: Senta Moses.

Dylan's responsibility to the patient extends far beyond the hospital when he declares war on a lethal street drug that nearly claimed the life of a young woman; Lu encourages the two caretakers of an injured child to end the blame game and start looking at the bigger picture; and Lana is offered the chance to put her college degree to good use, exploring the psychological aspects of women's health issues. Abigail Morton: Dorie Barton. Natalie Pascal: Danica McKellar. Marisol: Martha Millan.

Lu takes a personal interest in an 11-year-old boy with a history of behavioral problems who suffered a cardiac arrest at school after a teacher used a stun gun to discipline him; Dylan employs a risky measure when treating someone with a rare form of multiple sclerosis; and Kayla contacts the U.S. Department of Homeland Security when she suspects her patient has been exposed to the deadly poison ricin. Principal: Carl Gilliard. Shay Williams: Tequan Richmond.

Dylan's college mentor flies in from San Diego to seek treatment for a debilitating neurological disorder. While in Philadelphia, she clashes with Lu over the question of whether women are inherently less able to succeed in science. Also, a heartbreaking choice must be made by a female firefighter whose two children are dying from kidney failure. Dr. Ann Nanji: Kavita Patil.

After diagnosing three prep-school students with Legionnaires' disease, Dylan has difficulty identifying exactly how they contracted the illness. Meanwhile, Lu fights against inadequate health care at the women's prison where she volunteers. Josie Weaver: Tara Buck. Anita: Polly Cusumano. Nina: Sasha Perl-Raver. Paramedic Newton: John Griffin. Charlie Rumnock: Jon Spinogatti.

The arrival of twins brings twice the heartache when one of the newborns tests positive for cystic fibrosis, leading Lu to question who really fathered the children. Elsewhere, Dylan tries to help a female high-school placekicker on steroids after her father makes her stop cold turkey. Terry Garutso: Becky Wahlstrom. Elliot Jansen: Graham Sibley. Yesenia Barrera: Darlena Tejeiro. Paramedic Gordon: Jon Hershfield. Nurse: Racheal Seymour.

Dylan has reason to believe that he's a daddy when an old summer love and her teen daughter arrive at the hospital for care; Lu counsels a brain-dead patient's family as they make some very difficult decisions.

Dylan's new girlfriend, Sonja, comes under scrutiny from his teen daughter. But before he can ease tensions between the two, Sonja's in the middle of a health scare when she is hospitalized with symptoms of avian flu. Also, Lu has trouble determining the cause of a young patient's excess weight gain and takes issue with a government agency that is looking to bring the girl's mother up on abuse charges for overfeeding the child.

The Rittenhouse staff celebrates Lu and Jonas's wedding day. Meanwhile, Dylan must cope with a heavy patient load while also dealing with his daughter's latest act of teen rebellion. Araya: Eileen Boylan. Judge Hackney: David Clennon.