The docs console Izzie over Denny's death, and Meredith faces a decision about what to do romantically in the wake of her prom-night assignation with Derek. Meanwhile, George seeks relationship advice from Derek while the two are quarantined because of a plague scare; Kate and Alex treat an infant found in a high-school girls bathroom; and Adele Webber (Loretta Devine) gives her husband an ultimatum: me or the hospital. Finn Dandridge: Chris O'Donnell.
As the interns campaign for Izzie's reinstatement, Cristina meets Burke's parents (Diahann Carroll, Richard Roundtree) under awkward circumstances. Meanwhile, Addison takes a break from her hospital duties; and a woman with lung cancer (Roxanne Hart) decides to start living. Finn: Chris O'Donnell. Mark Sloan: Eric Dane.
Cristina tries to help Preston cope with his hand tremor; Izzie attempts to return to the hospital for the first time since she quit the program; Alex treats a foster child (Abigail Breslin) with an incredibly high pain threshold (and long history of injuries); and George wants Callie to move out of Meredith's house. Finn: Chris O'Donnell.
As Mark Sloan (Eric Dane) joins the staff, Addison, who's not at all happy about it, comes to doubt her medical skills. Meanwhile, Cristina pushes Burke's rehab; Meredith has a personal medical emergency; and Izzie gets a surprise. Fred Ward guest stars as Denny Duquette's father.
Bailey treats a young mother with breast cancer; Derek learns more about Addison's relationship with Mark, and finds out that Meredith broke up with Finn; the interns defend Bailey at an M&M meeting on Denny's death; and Meredith and Addison must extricate a divorced couple who find themselves together again. Meanwhile, Izzie has yet to cash Denny's $8.7 million check.
Derek receives a surprise visit from his sister (Embeth Davidtz); Cristina scrubs in for a rare procedure, to the envy of her peers; Addison and George treat a pregnant woman with an unusual problem; and Alex ponders his future in medicine.
The men of Seattle Grace go on a camping trip together; Addison and Callie team up on a case; Meredith assists Mark Sloan with a procedure unlike any she has experienced; and Bailey confronts Cristina on her recent actions at the hospital.
George's ailing father (George Dzundza) needs heart surgery; Meredith is determined to have a more positive outlook on life as she treats an injured girl who's closer to her nanny than her working mom; Derek and Addison try to be civil to each other; Izzie and Alex try to redefine their relationship as they work together; and Richard endeavors to reunite with Adele. Ellis Grey: Kate Burton.
Victims of a serious traffic accident fill the ER. Meanwhile, Cristina battles guilt about hiding Burke's tremor; Izzie tests the bounds of her probation; and George calls in Burke's med-school rival, Dr. Erica Hahn (Brooke Smith), for a consult on his father's operation. Harold O'Malley: George Dzundza.
Burke and Cristina's relationship is strained; Meredith's half sister, Molly (Mandy Siegfried), is admitted to the hospital; and Mark and Derek must work together when two close-knit brothers seek medical help.
Part 1 of 2. After a successful heart operation, George's father (George Dzundza) undergoes cancer surgery; Thatcher Grey (Jeff Perry) visits the hospital to see his new granddaughter; and Meredith discovers that Derek isn't a sound sleeper. Meanwhile, Izzie befriends a snippy teenager (Mae Whitman) with a severely curved spine; and George bugs Izzie to deposit that $8.7-million check. Louise O'Malley: Debra Monk.
Conclusion. As Harold O'Malley (George Dzundza) fights for his life following his cancer surgery, Meredith confronts her father (Jeff Perry) about his breakup with her mother, and an anonymous donor pays for Heather's spinal operation.
Rumors of the chief's retirement spread around the hospital; Bailey proposes the creation of a free clinic; and other Seattle Grace doctors receive proposals of a different sort. Meanwhile, a young Amish woman (Jessica Stroup) with cancer must choose between her parents and her best friend (Rachel Boston), who has been shunned by her community back home.
As Cristina weighs her marriage proposal, Ellis (Kate Burton) experiences a change in her medical condition; and a surgical patient endangers the lives of her surgeons when her blood becomes toxic. Meanwhile, the Denny Duquette Memorial Clinic opens; and George and Callie return from Las Vegas with a surprise.
The beginning of a three-part story arc in which a ferryboat disaster poses stern challenges to the interns. Meanwhile, Cristina has trouble telling Meredith that she and Burke are engaged; and Sydney (Kali Rocha) decides she wants to be chief resident.
Meredith remains missing after falling into the water at the site of the ferry disaster, where Izzie must perform delicate brain surgery on the fly while taking instructions from the chief over the phone. Back at the hospital, Alex struggles to match unidentified victims with anxious family members while George searches frantically for a 7-year-old boy after telling his injured mother he was safe just before she went into surgery.
As Bailey, Burke, Addison and the chief work feverishly to save her life, Meredith receives affirmation from an unexpected source. But Cristina can't cope with the prospect of her “person” not pulling through. Meanwhile, Alex begins to bond with the Jane Doe (Elizabeth Reaser) from the ferry; and tensions surface between Izzie and Callie---and Izzie and George. Dylan: Kyle Chandler. Denny: Jeffrey Dean Morgan. Bonnie: Monica Keena. Liz Fallon: Anna Maria Horsford.
The race for chief heats up as a new competitor enters the race; tensions mount between Izzie and George; Callie must reveal a big secret; Derek treats a patient close to him; and Alex continues his work with Jane Doe (Elizabeth Reaser). Helen Crawford: Shohreh Aghdashloo.
George meets his new father-in-law (Hector Elizondo), but is in no condition to make a good impression; Alex helps Jane Doe (Elizabeth Reaser) determine how she'll look from now on; the hospital board interviews candidates for the chief's position; and Izzie wrestles with a startling revelation about a close friend. Doug Kendry: Michael Boatman. Cathy Rogerson: Catherine Dent. Colin Marlow: Roger Rees.
George comforts Izzie as she faces her painful past; Derek questions his relationship with Meredith while she must decide what sort of relationship she'll have with her stepmother (Mare Winningham); and Cristina decides to fight for her relationship with Burke, despite her history with Colin Marlow (Roger Rees). Meanwhile, Alex grows more attached to Jane Doe (Elizabeth Reaser). Joan Waring: Dee Wallace.
While the interns cram for an exam, the attendings jockeying to succeed Webber as chief offer the very best of care to a very important patient: the hospital's board chair. Meanwhile, Burke plans his wedding without much help from Cristina; things heat up between Alex and Addison; and Derek questions his relationship with Meredith. Larry Jennings: Mitch Pileggi. Dr. Sydney Heron: Kali Rocha. Jane Doe: Elizabeth Reaser.
Addison takes a leave of absence to visit old medical-school friends in Los Angeles; Meredith's stepmother (Mare Winningham) arrives at the hospital with hiccups; Cristina reluctantly plans her wedding, with the help of her mother (Tsai Chin) and Burke's mom (Diahann Carroll); and Derek must perform emergency surgery on Ava as Alex continues to lend emotional support. Paul Adelstein, Amy Brenneman, Tim Daly, Taye Diggs, Merrin Dungey and Chris Lowell make guest appearances.
On the day before Burke and Cristina's wedding and the day of Susan Grey's funeral, the attendings treat injured mountain climbers while the interns take their first-year exams. Meanwhile, Cristina struggles to write her vows; George learns he has been accepted at another hospital; Adele (Loretta Devine) shows up at the hospital unexpectedly, as do Joe (Steven W. Bailey) and his partner, Walter (Jack Yang); and Ava (Elizabeth Reaser) regains her memory. This isn't good news.
Cristina and Burke's wedding day arrives, as do the final-exam results for the interns. Meanwhile, George and Callie arrive at a decision about their future as a couple; Adele Webber has emergency surgery; the husband of Rebecca Pope (formerly Ava) shows up; and Richard names his choice for his successor. Jeff Pope: Jason London.