Masters of Sex: Season 4

Betty struggles to keep the clinic afloat as the Masters and Johnson partnership appears to be dead. Masters' legal woes continue to pile up. Johnson attempts to publish a column through Hugh Hefner. Hefner sees this as an opportunity to reunite the sex experts. Libby expresses her rage against Masters.

Masters and Johnson return to work and fulfill their commitment to hire new partners for both of them: Masters hires Nancy Leveau (Betty Gilpin) as a partner and Johnson goes through several candidates before ultimately hiring Art Dreesen (Jeremy Strong). Libby gets a job.

Alice Logan (Judy Greer) returns and informs Masters that Johnson never married Dan Logan. Masters assembles his legal team. Johnson continues a self-destructive spiral. Nancy and Art's marriage is exposed.

Art and Nancy host a swingers party attended by Masters, Johnson, Betty, Libby, and Lester (all of whom unaware of the kind of party they are at). Masters and Libby reexamine their marriage. Johnson confronts her feelings toward Masters.

Masters and Johnson go to court to settle their outstanding legal case. Masters rekindles his relationship with Libby. Johnson attempts to salvage their book deal. Art and Nancy discover that the clinic is being bugged. Helen must conceal her relationship with Betty from her conservative parents.

Johnson makes continued attempts to rekindle her romance with Masters. Masters and Johnson suspect that their book agent is a closeted homosexual. Nancy and Johnson's disagreements reach a boiling point. Helen goes into labor. Libby visits a nudist colony.

Masters gives Art authority to begin studying homosexuals. Johnson and Nancy investigate self-proclaimed sex gurus stealing the clinic's techniques. Masters' AA sponsor (Niecy Nash) requests help reinvigorating her sex life with her paraplegic husband.

Masters and Johnson go undercover to investigate charlatans pirating their methods. Masters uses this trip to reconnect with a past lover (Kelli O'Hara). Nancy takes advantage of their absence by developing a plan to start her own clinic with Art. Libby considers going to law school.

Masters learns that Louise has fallen off the wagon. Johnson is distraught to hear that her parents' marriage is crumbling. Libby and Bram get caught in traffic. Nancy lies to Art regarding her pregnancy.

Series finale. Masters and Johnson announce their engagement. Nancy's competing business venture is exposed. Masters and Johnson signal to their publisher that they are open to the study of conversion therapy, although their first "success" story appears to be anything but. Libby leaves for California.