Meredith and Derek feel torn about work as they stay home with their newborn son. Elsewhere, Arizona attempts to repair her marriage; Alex and Jo adjust to being a couple; Owen and Jackson disagree about finances; and April awaits crucial test results.
The hospital holds a fund-raising event, which takes on a competitive twist thanks to Jackson. Meanwhile, Bailey treats some demanding patients; Shane and Stephanie attempt to manage a chaotic ER on their own; and Alex exposes his vulnerable side to Jo.
Meredith struggles to balance her work with motherhood. Elsewhere, Stephanie strives to impress Jackson's mother; Jo gets too attached to a patient; and Callie and Owen get wrapped up in an emotional dilemma concerning a patient.
Derek and Callie team up for a brain-mapping project while Meredith contemplates continuing her mom's research. Elsewhere, Richard proposes that his physical condition be used as a learning tool; and feelings of guilt about Heather's death plague Shane.
Eerie patients arrive at the hospital on Halloween, and one of them puts a doctor's welfare at risk. Meanwhile, Derek and Ben team up for a new surgical procedure; and Richard requests that a second-year resident perform his surgery, infuriating Bailey.
Strife builds between Meredith and Cristina, leading to a shocking betrayal. Elsewhere, Derek advises Jackson to step back and let other doctors tend to his patients; April and Matthew make a big decision; and Ben's return complicates things for Bailey.
Ben regrets a conversation he had with Derek, fearing it may lead to problems for Bailey. Elsewhere, Cristina finds a friend in Shane; April's wedding plans cause awkwardness for others; and Meredith decides to host Thanksgiving dinner.
April's sister visits and begins to annoy her. Elsewhere, Callie and Arizona put effort into a reconciliation; Matthew and Jackson join forces after they see a devastating accident; and Cristina is urged to live stream video of an operation.
April's wedding day arrives. Meanwhile, Meredith and Cristina continue to clash; Bailey tells Ben how she honestly feels about his return; Shane inserts himself into a perilous situation; and Derek receives a life-changing phone call.
Alex hears news about his dad and becomes angry. Meanwhile, Derek doesn't keep a promise, leaving Meredith feeling betrayed; Arizona and Callie make a decision about their relationship; and Bailey uncovers the real reason why Ben returned to Seattle.
A nonfraternization policy is issued to hospital staff in the wake of a complaint, leading the couples to worry about their relationships. Meanwhile, Emma and Owen discuss the future; and Richard asks the residents to research an atypical cancer case.
Arizona advises a patient who's facing a potential double amputation. Meanwhile, Derek doesn't fulfill a promise to Callie; a baby is abandoned outside of the hospital; and a doctor gets suspended for not adhering to the nonfraternization policy.
Meredith gets an assistant to help with her vein project. Meanwhile, Richard receives a special birthday gift from Bailey when she allows him to scrub in on an extraordinary case; Callie surprises Derek; and a young pregnant mom seeks help from Shane.
The doctors get sick after flu patients flood the hospital. Meanwhile, Derek must deliver an important speech on brain mapping, despite feeling ill; and a new doctor introduces Alex to a different way of practicing medicine.
Cristina is nominated for a prestigious award and remains calm amid all of the excitement. Meanwhile, Bailey tries to help a boy who doesn't have an immune system; Derek and Callie use a machine that recognizes emotions; and Richard delivers a pep talk.
Pressure mounts for Derek both at work and home. Meanwhile, Meredith helps Cristina write an acceptance speech in case she wins an award; April and Jackson are at odds over big marital issues; and Callie and Arizona attempt to reestablish their bond.
The doctors receive bad news from Jackson. Meanwhile, Amelia arrives in Seattle for an unexpected visit; Richard heads to Boston to surprise Catherine; and Bailey makes a bold decision after growing disappointed with the lack of progress in her research.
Cristina seeks guidance from Meredith as she makes a decision about her future. Meanwhile, Derek and Amelia join forces to operate on conjoined twins; Jo takes on too many cases; and Stephanie uncovers the truth about Bailey's bubble-boy case.
Amelia opens up to Meredith about her time in Seattle. Elsewhere, bad news is delivered to Callie; Bailey faces the consequences of her actions; and the residents are alarmed to hear that one of them will soon be out of a job.
In the 10th-season finale, Cristina's coworkers give her a fond send-off. Meanwhile, a possible terrorist act occurs in Seattle and leads to pandemonium at the hospital; Meredith makes a life-altering choice; and a doctor gets alarming news.