Abby, Pratt and Morris cope with Dr. Morretti’s new ER procedures, which are more strict than what they are used to. As injuries from an anti-war rally roll in, Gates worries about Neela and takes issues into his own hands when he learns who was behind the rally explosion.

Dr. Morretti continues to implement new measures that lead many of the doctors to despise him. A teacher and student arrive at the ER after a car accident, and Morris and Sam are shocked when they find out why the two were together. Abby treats a patient with a stomach ache, but finds that there may be more to the ache than meets the eye.

A teen wrestler comes to the ER experiencing severe vomiting and Pratt finds that the cause of the problem is very serious. In ICU, Gates tries to help a young child with a deadly disease. Meanwhile, Abby and Morris help two volunteer cops shot in the line of duty.

County General is unwittingly turned into a beauty parlor when a former patient decides to give beauty treatments to patients. Meanwhile, Abby is saddened when baby Joe is brought in following a fall off of the jungle gym; Gates helps a young boy's dream come true; and Pratt tries to defend his brother, but ends up making things worse in the process.

Moretti determines that since Gates has been impressive in ICU, he is ready to return to the ER. Neela is assigned to mentor Harold, a young genius intern. Meanwhile, Abby struggles without Kovac and Morris has a hard time resisting other women while Hope is away.

Morris and Pratt study for their board exams and Morretti brings in an attending to help with the load. Sam and Abby work with a young woman with elusive symptoms.

In the midst of the go green craze, Morris buys a new energy-efficient car. Abby and Pratt disagree on the diagnosis of a fussy baby. Later, Abby falls back into old bad habits while Kovac is away in Croatia.

Gates and Julia are enjoying their new relationship, but are thrown off when they get a disturbing call from Sarah. Abby’s struggles with Kovac gone begin to worry the staff, but she soon receives an unexpected surprise. Meanwhile, Harold is the hero in a critical situtation.

Kovac's brother arrives from Croatia to visit, which causes Abby to feel crowded. Gates begins to feel the pressures of being a father when Sarah has a sleepover. Meanwhile, a temporary ER chief is named, much to Pratt's dismay.

In ER's landmark 300th episode, Luka and Abby arrange to head off to Croatia following the death of Luka's father. Meanwhile, a man learns his wife's startling secret while she is about to pass away, while the ER staff reminisces on past patients throughout the years.

After being passed over for ER Chief, Pratt makes plans to leave County and go to a hospital that will appreciate his talents and take him more seriously. A woman comes in with a severely injured ankle and a terrible secret, and Sam finds herself closely identifying with her. A former ER staff member rushes in to be with her son, who was brought in after a fall during gym class. Neela’s cousin is in town, and Morris and Harold vie for her attention.

Abby feels like she is being judged by her peers as she returns from a stay at rehab. Meanwhile, she treats a fire victim who's eyes may have been damaged, and Harold's night with Neela's cousin has given him an ego boost.

Neela's journey into Orthopedics means teamwork when she joins their hockey team. Pratt is uncertain about moving his relationship with Bettina forward. Sam and Gates are at odds while Julia assists a prison doctor with a guilty conscience.

Dr. Pratt and Dr. Brenner get off to a shaky start when Brenner refuses to teach the interns. Meanwhile, Dr. Gates treats a transplant patient who is having heart issues. Abby debates telling Kovac about her affair and Sam learns of Gates and Julia's break-up.

Neela has an odd daydream at work after working an all-night shift. Sarah's grandfather has to be taken to the ER when he collapses during an air hockey game. Meanwhile, Gates tries to prove himself to Sam by sending her flowers and Neela must make a quick decision when a patient suffers a torn aorta.

An upbeat cancer patient has a great impact on Luka as he searches for work as a hospice care worker. At County, a patient of Neela's comes down with an infection caused by her aorta surgery. Meanwhile, Abby treats a beating victim, and Brenner continues to belittle the ER staffers.

Pratt hopes he can salvage his relationship with a wary Bettina. Meanwhile, Neela feels her patients may be criminals, and Abby fears that Luka is has quit on their marriage.

Neela is under great pressure after her patient needs more follow up surgery. A run-in with thieves has Morris visiting a therapist, and Abby must make a tough decision when offered a great opportunity.

Everybody at County are endangered by the actions of a drunken patient. Also, Pratt moves closer to becoming the new chief resident; gates worries about his budding relationship with Sam; while Kovac and Dr. Moretti have an unexpected encounter.