Benton is hailed as a miracle worker after he seemingly heals a blind man. Corday operates on Allison Beaumont again. Mark discovers Cynthia’s hidden past. Carter discovers his cousin Chase shooting heroin. Mark treats an elderly rape victim, learning about forgiveness. Weaver is apparently seeing Ellis West. Carol and Doug announce their relationship to the staff. Carter signs off on George Henry’s internship after performing an intubation on a patient that was already dead.

Season Premiere. The ER is under the bright lights when a television documentary is filmed depicting a typical day in the ER. British trauma specialist Elizabeth Corday joins the staff. Carter restarts his residency, this time in the ER. A man is paralyzed while breaking up a gang fight. Morgenstern suffers a heart attack. Mark’s stress level continues to build.

Dogged Debra’s investigative skills have the department on the verge of not only nailing the Trinity Killer, but ultimately exposing Dexter’s clandestine and deadly side job. It would also deprive him of the opportunity to deal with the serial murderer in his own way. At home, Rita’s decision to confide in her husband doesn’t garner [...]

As Thanksgiving, Christmas and New Year’s pass, Miranda gets a visit from her father, William who disapproves of her choices in life. Mark and Lexie cope with an arrival of a woman from his past. Thatcher questions the Chief’s recent behavior as Meredith comes to his defense.

Owen recruits Dr. Teddy Altman a former Iraqi veteran, as the new cardiothoracic surgeon, Cristina questions her abilities in the E.R. and relationship with Owen. Izzie returns to Seattle Grace with her high school mentor seeking treatment for his dementia. Richard’s responsibilities, post-merger, are taking a toll on him.

A generous 25 million donation is offered to Seattle Grace by the parents of Arizona’s 10-year-old patient, she finds herself in a conflict of interest when his condition worsens. Cristina tests her boundaries with Owen at the hospital. Alex is left with all of Izzie’s hospital bills to contend with.

When the hospital lab tech, Isaac, discovers he has an inoperable tumor wrapped around his spine, he turns to Derek for help; Derek challenges Richard’s authority.

When a burn victim unexpectedly dies in the E.R., all the Mercy West and Seattle Grace residents must defend their actions in hopes of saving their jobs.

The residents of Seattle Grace and Mercy West vie for surgeries and their careers as day one of the hospital merger begins. Meanwhile, Arizona stands by an enraged Callie when her father, Mr. Torres, employs a priest to help convince her to date men, and Izzie experiences the brunt of her new surgical competition.

When Meredith and Lexie’s father, Thatcher, returns to the hospital with a failed liver, it’s up to Meredith to save his life. Meanwhile, Izzie empathizes with a patient riddled with tumors, as Mark, annoyed with Cristina’s competitive zeal, tricks her into assisting on an unusual surgery.