Pete, Violet, Sam and Addison adjust to their new, singles lives in different ways. Addison questions how much she wants a baby and confides in Jake, Violet considers an offer to go on a date with a young, hot paramedic, and Sam and Pete have a bachelors' night at a local bar. Meanwhile, Charlotte faces a personal, ethical dilemma when Amelia uncovers a secret about Mason's mom, Erica, and Sheldon refuses to bend to the pressure when an old friend from the police force wants him to rubber stamp a fellow cop suffering from PTSD.

Violet steps in to the middle of a dangerous situation.

Sheldon counsels Sam's friend, Rick, an Army veteran suffering from PTSD who harbors a secret sexual trauma; Erica and Mason are involved in a car accident that forces Cooper and Charlotte to further come to grips with their future; Violet and Pete struggle to navigate life after marriage when he finds her kissing Scott; and Addison and Jake attend a medical conference they won't soon forget.

Sam finds his estranged sister, Corinne, in jail, heavily medicated and near-catatonic, and brings her to Sheldon for help; Erica begins secret treatments for her cancer and refuses to let Cooper and Charlotte tell Mason; Cooper, Pete and Addison treat the baby of a drug addict; and things between Violet and Scott continue to heat up in the bedroom.

Cooper and Charlotte take Erica to Seattle Grace to meet with Derek, Lexie and Amelia regarding a very risky surgery; Scott tells Violet that he would like to take their relationship to the next level; and Addison finds herself caught in the middle of Sam and Jake's fight about a patient. Meanwhile, Sheldon warns Sam to be cautious as he deals with the return of his sister, Corinne.

Sam tries to take care of his sister, Corinne, but her mental condition makes that nearly impossible; Sheldon learns that Amelia has life-changing news; the flirtation between Addison and Jake continues, and Cooper rejects Charlotte's suggestion to seek outside help with Erica's care.

Sheldon warns Sam that he may be in over his head when he insists on releasing Corinne from the hospital and caring for her at home; a badly beaten Scott arrives at the ER and is placed under the care of Pete; Amelia is encouraged to make a decision about her unborn child; and Jake's daughter grills him on his love life when he visits her at college. Meanwhile, Erica's health takes a turn for the worse.