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.

A mysterious, fast-acting and extremely deadly virus triggers an emergency lockdown on the 6th floor of Westside Hospital; in an effort to save a crashing Richard from a deadly virus, Amy gets infected with it.

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.

After a tragic accident, one of Joan's oldest friends is rushed to Minneapolis to be treated by her, forcing Amy to confront her about her illness. Richard and TJ find themselves at odds when they treat a tech bro who thrives on pushing boundaries. Michael tries to pick up the pieces in the wake of his fractured marriage.

Met with hostility upon his return, Richard looks to redeem himself while treating an overworked food delivery worker. Sonya and TJ enlist Jake's help with the delicate Joan situation. Amy and TJ take on the case of a well-known medical malpractice lawyer, leading to unexpected complications.

While navigating the fallout from Katie's secret, Amy treats a critically ill patient with a dark one of her own. As Gina and Jake evaluate a world-class poker player, searching for the source of what may be a mental disorder, Jake is forced to hide the truth from Amy about Rachel's health scare. Sonya and TJ investigate their theory behind Joan's frequent absences. And Richard returns with a trick up his sleeve.

Charlie fights for his life at Westside with Hannah by his side. The Board launches an internal investigation into Brian Clark's resignation, putting everyone in the hot seat and motivating Amy to figure out what happened before the hospital can make her a scapegoat. A familiar face returns to Westside and Amy is not happy about it.

Gibbs and the NCIS team have to find answers regarding Tony's months-long assignment when an NCIS agent is found dead.

While investigating the murder of a Navy Commander, the NCIS team finds out the whereabouts of Agent E.J. Barrett.

Terrorism shakes the foundations of the Navy and NCIS to such an extent that Gibbs and the team face surprises that will devastate them.

Zack is upset at Kelly after their breakup and tries to make her feel bad. The gang is caught in the middle. Lisa plans her Sweet Sixteen party.

The Costume Ball is coming up and Zack and Kelly plan to go as Romeo and Juliet. Kelly gets a job at the Max, and her boss, Jeff, comes between her and Zack and they break up.

Zack meets a college girl and tells her he goes to USC and is studying photojournalism. Screech makes fake IDs and the guys sneak out to meet her at the over-18 nightclub "The Attic." They're in for a surprise when it turns out Kelly's boyfriend Jeff also likes hanging out there...without Kelly.

The gang joins the Glee Club in hopes of winning a trip to Hawaii, but Screech's girlfriend, Violet, is the only one good enough to get them there. Screech makes a bad impression on her parents and is forced to quit the Glee Club and stay away from Violet, but when she freezes onstage, he saves the day.

Jessie and Slater break up over anniversary ballet tickets, then Kelly and Zack break up when her ex-boyfriend comes to town, so Belding tries to get them back together, until he has fight with Mrs. Belding over his mother-in-law. Zack and Slater have to come up with a way to win back their girlfriends.

After Jessie's Mom remarries, Jessie's step-brother, Eric, arrives in town from NYC, and he has more than just Jessie annoyed when he uses blackmail to get what he wants from the gang.

The school holds a dance-date auction to pay for new cheerleading uniforms, where Zack, Slater and Screech are up for auction; Jessie is appalled at the whole idea; Lisa becomes an intellectual to impress a smart boy. Zack is paired with Wendy, an overweight girl, and acts like a real jerk.

It's time for the school play and the gang decides to do a revamped rap version of Snow White and the Seven Dwarfs, substituting Dwarfs with Dorks. Zack and Jessie start to wonder if they have feelings for each other and Kelly and Slater get jealous.

Zack is in charge of filming the Bayside video yearbook, which he came up with as an alternative to regular yearbooks that nobody would buy. When he realizes that using the tapes to make a dating tape that he can sell for money to buy a car, he thinks it's a great plan, until it backfires and all the girls at Bayside have dates with other guys at other schools.