Violet's emotional reaction to her attack has all her friends on standby alert, afraid she'll freak out. Addison makes no effort to ease tensions between her and Naomi, while the practice tries to deal with a woman they feel is covering up something when her husband shows up at the hospital with a stab wound.
Dr. Miranda Bailey shows up in California with a pair of patients in tow; a donor and her recipient sister, a young lady who needs a kidney transplant within 72 hours in order to survive. Addison gets blind-sided by Noah's wife and Pete gets blind-sided by Violet when she agrees to grant Sheldon a paternity test.
Addison and Sam make some decisions about the practice that forces Cooper to take stock of his financial situation, while all three doctors get involved with a homeless teen mother and her young son. Violet continues to push away the people who are closest to her, all the while letting what's happened to her affect them and her work, as well.
Addison must deal with the return of Naomi's former patients, Zoe and Amelia, whose embryos were accidentally switched, and a serious complication that may end up jeopardizing both fetuses. Meanwhile the time has come for Katie's trial, as Violet struggles with whether or not she can face her attacker in court, and Charlotte is determined to convince Addison, Sam and Cooper to let her join Oceanside Wellness Group.
The doctors venture into controversial territory when an unexpected new hire at Pacific Wellcare causes Naomi to struggle with the idea of genetically designing babies and Violet makes a sudden decision to try electric shock therapy on a patient. Meanwhile Addison somehow finds herself alone and with a cat.
Addison and Sam go for a hike in Malibu, and must perform urgent field care when they stumble upon an expecting couple, trapped in their car after an accident. Meanwhile at Oceanside Wellness, Charlotte, Cooper and Violet treat a newlywed who, out of nervousness for his wedding night, has taken too much Viagra, and Pete and Sheldon hit the bar scene together but fall for the same girl.
Addison is shaken by the unwelcome arrival of her father to Los Angeles, Cooper is arrested when he refuses to cooperate in a case involving a longtime patient, and Pete fights to keep a terminally ill patient alive long enough for him to meet his new daughter.
Addison performs a complex in utero surgery, proving not only her talents to her father but also finally giving them some common ground. Meanwhile Sam and Naomi deal with their own family crisis when they discover their daughter is growing up way too fast, and Violet does the unthinkable.
A terrible explosion at Dell's house lands Betsey and Heather in the hospital, and everyone is pushed to the limit trying to save their lives. Tensions rise even higher between Addison and The Captain when her mother, Bizzy, shows up and a shocking family secret is revealed.
Desperate to help his pregnant daughter, Mark follows Addison back to Oceanside Wellness, Dell and Naomi struggle to raise their children under the same roof, and Violet and Cooper heatedly disagree on how to treat a patient on.
Sam isn't happy with the way Maya is proposing to deal with her problem and Naomi won't talk about it at all, but Sam is dying to talk more to Addison about the sparks between the two of them and Addison doesn't want to deal with that. Following the fall out between Cooper and Charlotte, Violet offers her home for Charlotte, which doesn't exactly thrill her best friend. Patients include twin girls who are terminally ill and their little brother is only able to save one of them.
Sam convinces Violet to help plan Maya's wedding when Naomi refuses to take part, tensions between Addison and Sam rise even as they work together to treat a suicidal patient, and Cooper and Pete treat a teenage girl with a mysterious bite mark on her neck.
As Violet continues to help Sam with Maya's wedding, Naomi refuses to take part as she works with Addison and Pete to save the life of a 25-week-old premature baby. Meanwhile, Cooper suspects that Charlotte's new boyfriend is abusing pills.
Things get too close for comfort when Addison, Pete and Sam must come together on a complicated case involving a dad-to-be who comes down with tuberculosis and threatens the future of his new family. Meanwhile, with Violet still gone on her Costa Rican escape, Sheldon takes over helping one of her patients, Natasha, to get over her crippling fear of flying, and Naomi finds herself in a bit of a love triangle of her own.
Addison clashes with Sam's new girlfriend Vanessa over the treatment of her patient Kayla - a surrogate carrying triplets for a childless couple. Meanwhile, Naomi's tangled love life between William and Gabriel gets more intense just as Pete notices that William appears to be having health problems. Elsewhere, Cooper and Sheldon argue over Charlotte as they treat a young girl who may be suffering from schizophrenia.
A husband's decision to pull the plug on his pregnant wife is overruled by a judge, forcing the hospital to keep her on life support until the fetuses she is carrying as a surrogate are able to survive. Meanwhile, Naomi feels betrayed after learning of Sam and Addison's feelings for one another, and she turns to Dr. Fife for support while William is away on business. And unable to cope with the tension, Addison takes the day off with Pete and Lucas.
When famed neurosurgeon Dr. Ginsberg and her team pay a visit to St. Ambrose to save the life of Kayla, Addison is shocked to see Amelia Shepherd - Derek's younger sister on the team. But Amelia's presence causes strife between Addison, Sam and Pete when she claims she can save Kayla's life after Dr. Ginsberg declares nothing can be done. Meanwhile Charlotte seeks from Cooper's with a sex education seminar for the elderly that only leads to more tension between the two, as they try to figure out how to work together.
After her open-ended escape to Costa Rica, Violet has finally returned home and to the practice. Everyone treads a little lightly around her, especially Pete and Addison who have mixed feelings about Violet's desire to reconnect with Lucas. Meanwhile Amelia butts into Sam's personal life, pointing out that he can mend hearts in the OR but can't seem to do that for himself; and Sheldon encourages Charlotte to reconcile with Cooper, while Cooper deals with a young patient who eats everything in sight.
Naomi puts Fife in a conflicted position when she begs him to help William's advanced ALS with his still experimental treatment. Meanwhile Violet and Amelia treat a woman with a brain tumor who has to choose between life or quality of life, and Sheldon decides to officially throw his hat into the ring for Charlotte's affection
Maya and her unborn baby are fighting for their lives on the operating table, and Addison, Amelia and Fife try everything humanly possible to save them. Meanwhile, Sam operates on an incoming crash victim and later makes a grim discovery; Cooper makes an ill-timed but valiant effort with Charlotte, and the staff's world gets rocked by an unexpected death.