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.
Pete and Violet anxiously prepare for their wedding day, but Cooper may have to intervene when emotions and fear of the future run high. Things have taken a surprise turn with Addison and Sam, and Naomi juggles the burden of caring for her daughter and newborn granddaughter and worries about Dink's ability to parent. Despite disagreements and deeply-rooted conflicts, the doctors come together to mourn the loss of their friend, Dell.
Violet and Cooper make amendments to their friendship in order to please their significant others; Pete and Cooper get in an argument involving marijuana use by a patient (guest starring Justine Bateman as Sydney); Addison is conflicted about going public with her new romance, and Sheldon's decision to deny approval for a patient's sex change backfires.
The man responsible for endangering Maya's life and killing Dell shows up at Oceanside Wellness with a heart condition, and Sam struggles with his responsibility to help; contrary to Violet's warnings, Pete volunteers at a friend's home medical clinic and ultimately puts a patient's life at risk; and news of Addison's new romance doesn't go over well.
The arrival of Dell's young orphaned daughter, Betsey, stirs up the emotions of everyone in the practice; and Pete and Amelia disagree over a risky surgery to treat a woman who has been experiencing chronic and insufferable pain throughout her pregnancy.
Much to her displeasure, Addison is teamed with a new oncologist, Dr. Rodriguez, to treat a newborn baby with a malignant tumor; when Violet and Sheldon visit a prison in order to interview inmates who are up for parole, Pete is highly uncomfortable as Violet tries to help a parolee; and Addison and Violet suggest Sheldon could be the solution for Amelia's needs.
Addison and Sam's relationship is strained when they disagree over the treatment and safety of a comatose patient who has become pregnant, while Pete and Charlotte are faced with the ethical dilemma of revealing the HIV status of a patient who has been in a serious auto accident. Violet crosses some boundaries with Pete's family as she gets caught up in the fray of Lucas's first Halloween.
After Pete discovers Charlotte in the halls of the hospital bloodied and bruised, he and their fellow doctors come to her aid, but only Addison learns the truth from Charlotte that she was sexually assaulted.
Charlotte chooses to suffer in silence as she tries to deal with the emotional aftermath of the attack, as Addison struggles to keep the events of that night a secret, while Cooper and the doctors of Oceanside Wellness fight their own demons arising from the assault.
Despite how Charlotte is choosing to deal with the aftermath of her sexual assault, her fellow doctors think they know what's best, teaming up to pursue criminal charges against her attacker. Pete gets a surprise visitor, his estranged brother, who has come to ask Pete to help release their sick mother from prison.
When the District Attorney's office delivers bad news to Charlotte and Cooper about her sexual assault case, Cooper is outraged and Charlotte seems numb, as a case involving a pregnant drug addict hits hard with Addison, who wants a child of her own with Sam.