Ben worries that an innocent conversation with Derek could end up causing problems for Bailey; Cristina turns to Shane as tension with Meredith increases; April's upcoming wedding creates an uncomfortable situation for Stephanie and Jackson.
The doctors face the consequences of the events that took place at April's wedding. Meredith feels betrayed when Derek goes back on a promise, Alex is furious after returning to the hospital and hearing the news about his father, and Arizona and Callie decide whether or not to move forward together. Meanwhile, Bailey realizes she was wrong about the motive behind Ben's decision to move back to Seattle.
Couples panic when the hospital announces a nonfraternization policy; Owen and Emma discuss the future; Meredith and Cristina have some girl time; Richard asks the residents for help with a rare cancer case.
Arizona's bad day escalates when she advises a patient on a potential double amputation; Derek breaks a promise; Stephanie and Jo find an abandoned baby; the nonfraternization rule leads to a suspension.
The doctors of Grey Sloan Memorial Hospital succumb to an infection that spreads like wildfire. Cristina deals with a complex case involving siblings and Alex begins to consider his future in the hospital.
Callie and Arizona discuss having another baby, Derek has a hard time juggling work and family, Jackson and April have their first big fight and Christina attends the Harper Avery Award Ceremony. But is she going to win?
The doctors work together to operate on two sisters joined at the head; Cristina travels to Zurich where she deals with a blast from her past; Richard voices his concern over the hospital's allegiance with the Harper Avery Foundation.
While Bailey faces dire consequences for her reckless behavior, Cristina interviews candidates for Dr. Russel's replacement. Alex returns with a motive, disappointment hits Callie and Derek brings forth a shocking proposal to Meredith.
Cristina must head to Zurich soon but she is unprepared to leave behind her life in Seattle. Fear runs amok throughout the hospital as an explosion in a shopping mall results in a mass casualty situation.