After a tragic accident, one of Joan’s oldest friends is rushed to Minneapolis for treatment, forcing Amy to confront her about her illness. Meanwhile, Richard and TJ find themselves at odds when they treat a tech bro who thrives on pushing boundaries and Michael tries to pick up the pieces in the wake of his fractured marriage.
When Amy and Michael take Katie on a road trip to her college orientation, they pass a familiar campsite and decide to stop and hike the trail. The journey quickly becomes harrowing when they discover an injured man whose life hangs in the balance. Stranded in the middle of nowhere, with no cell service, it's up to the three of them to somehow save him.
On her last day at Westside, Joan chooses an unlikely successor, crowns a Chief Resident and imparts some final wisdom to the next generation. Gina steps in to help TJ's patient, a foster child suffering from rheumatoid arthritis. Amy and Jake's tension intensifies while treating a pregnant teen caught between her divorced parents.
On Michael's first day as Chief of Internal Medicine, Joan arrives at the hospital as a patient in dire straits. Amy, determined to save her, clashes repeatedly with Richard over Joan's treatment plan. Meanwhile, Gina makes a nearly impossible medical decision for a young patient and Liz fights for her allegations against Richard to be taken seriously.
A mysterious, fast-acting and extremely deadly virus triggers an emergency lockdown on the 6th floor of Westside Hospital. In the face of seemingly insurmountable odds, everyone must work together to contact trace, triage and attempt to contain this terrifying killer. As fear grips the staff and patients alike, Amy pushes through debilitating memory seizures and races to find a cure before it’s too late.
In an effort to save a crashing Richard from a deadly virus, Amy gets infected with it. Michael and the team work tirelessly to help her and the other patients but their experimental treatments fail and Amy becomes critically ill. When a promising cure finally emerges, there isn’t enough to save everyone—forcing the team to decide who will live and who will die, as Amy’s life hangs in the balance.