Dr. William Masters, Washington University’s foremost OB/GYN, runs a successful medical practice by day and conducts a secret study of human sexuality by night. Former nightclub singer Virginia Johnson joins the hospital secretarial staff and proves herself to be an asset to Masters’ work.
On the heels of Masters’ proposal that they participate in the sexual response study, Johnson considers the best course of action to keep her job – only to find she no longer has one. The study has been forced out of the hospital and Masters believes Johnson is to blame. As Johnson fights to save her job and struggles to care for her kids, Masters moves his study to a brothel. But Masters soon discovers that the chaos of the cathouse is unmanageable without Johnson’s help.
Masters and Johnson continue their research in the brothel but skewed data confirms that Masters must get the study back into the hospital. At the hospital, Johnson is surprised to learn that a distinguished new doctor on the OB/GYN floor is a woman who has no interest in female solidarity. Meanwhile, Libby struggles to conceive and Dr. Ethan Haas gets the case of a lifetime – a woman pregnant with quadruplets.
With the study back in the hospital, Masters and Johnson recruit new participants on campus. But Johnson is shocked when her ex-husband George, who’s crashing on her couch, wants to sign up. Masters’ mother comes to visit, but her new take on life stirs up painful memories of his childhood. And Libby’s attempt at playing matchmaker with Virginia and Ethan doesn’t go as smoothly as she’d hoped.
When Masters and Johnson expand the study to include couples, they discover that the science of sex is easily complicated by the mystery of attraction. Johnson tries to connect with her son who prefers his dad. In anticipation of his baby’s impending arrival, Masters experiences anxiety about becoming a father. And Dr. Ethan Haas learns that dating the provost’s daughter could impact his medical career.
In the aftermath of the miscarriage, Libby and Masters travel to Miami for some much needed rest and relaxation, but Masters is drawn back into his work by a sexually adventurous couple next door. Alone in the hospital, Virginia enlists Jane in an effort to debunk Freud’s theory that one kind of female orgasm is better than another. And Langham finds an unlikely cure for his sexual dysfunction in Margaret Scully.
Masters and Johnson continue their sexual response study – now as participants – but Johnson fears their work may be interfering with Masters’ home life. Libby pressures Dr. Haas to resume her fertility treatments in secret. Meanwhile, Haas struggles to let go of feelings for Virginia as his relationship with Vivian deepens. And Margaret Scully, caught in her infidelity, confronts her husband on the mounting problems in their marriage.
Masters and Johnson decide that the best way to record their study findings is to film them, but to do so they have to enlist outside help. Johnson redoubles her efforts to get a college degree, only to find that Dr. DePaul’s Basic Anatomy class is a requirement. Meanwhile, Haas and Langham – both unsure in their relationships – convince each other of the merits of being a married man. And after Margaret catches him in a compromising position, Scully takes drastic steps to control his sexual impulses.
When Masters and Johnson decide to film external reactions in the study, they must convince Lester and Jane that their footage won’t cross the line into pornography. Haas and Vivian’s plans for a Presbyterian church wedding are sidetracked when Haas reveals he’s Jewish. Libby keeps her pregnancy a secret from Masters and instead encourages him to mend his relationship with his mother. But during late night visits to the hospital, Estabrooks observes Masters and Johnson’s intimate relationship.
The hospital takes part in a nationwide civil defense drill, and the heightened atmosphere escalates conflicts among the staff. A former study participant reveals she’s pregnant and wants to know the identity of the father. Masters and Johnson, their relationship strained after ending their study participation, butt heads on whether to maintain study confidentiality or take responsibility. Haas learns he’s been denied a future job at the hospital but wrongly assumes his breakup with Vivian is to blame. Margaret Scully seeks answers about her husband’s sexuality from an unlikely source.
With Johnson no longer on his team, Masters accepts Libby’s offer to help compile the study work for a hospital-wide presentation. But when Masters sees another doctor’s presentation put his colleagues to sleep, he becomes determined to grab their attention even if it means pushing through provoking, but incomplete, research. Dr. DePaul and Johnson travel to a medical convention and DePaul opens up on why her work on the Pap smear is so important. And Virginia’s ex-husband George returns to find Ethan Haas playing father to his children.
Masters’ work on human sexuality culminates with a hospital-wide presentation of his and Johnson’s research findings. But when Masters attempts to push the envelope with the external footage of the female orgasm, the doctors’ response to the film is not what he had hoped. Meanwhile, Haas entertains a job offer at UCLA Hospital and considers what a move would mean for his relationship with Virginia. Scully pursues electroshock treatment with the hope of curing his homosexuality but Margaret has second thoughts about the risks involved.
In the wake of their fallout, Masters and Johnson search for purpose in a world without one another and look to work as their personal lives crash down around them. Libby finds herself alone for the first time since her marriage and discovers some unexpected allies. Season premiere.
Masters and Johnson turn to new partners in an effort to put the past behind them and focus on their expanding clinic. Given their fractured triangle, Libby reevaluates her relationship with Bill and Virginia.
Masters and Johnson adjust to new partners, but their respective cases have them second-guessing the instinct to remain separated. A romantic prospect pushes Libby to embrace life as a newly single woman of the sexual revolution.
Johnson, Masters, Libby and Keller wind up together at a party thrown by Art and Nancy. Pairings and perspectives shift as the night wears on, until the light of day exposes the consequences of the evening.
Johnson and Masters' troubles come to a head as the trial begins with Keller leading the charge. Virginia does her best to revive their career as Bill faces the reality of what the charges could mean for him, Johnson and the practice.
Johnson looks to get her relationship with Masters back on track while Masters does his best to find satisfaction elsewhere. Betty and Helen ready themselves for a new addition; Art and Nancy discuss the consequences of their party.
Masters looks to groom Art as his protege in a new area of research as Johnson does her best to keep Nancy at arm's length. Betty seeks an unlikely source for assistance in her fight for equal rights to Helen's baby.
Masters and Johnson go on the road and pose as a couple to investigate practices at a competing clinic. While Bill and Virginia are away, Art, Nancy and Langham take advantage of their absence to further their own agendas.
Masters and Johnson return from Topeka, each grappling with the trip's ramifications. Art and Nancy look to tie up loose ends in order to have a fresh start, and Libby embarks on a road trip with Bram that changes her perspective.
Masters and Johnson work to save the practice from disintegrating in the face of insurrection within the clinic. As everyone in their lives either moves on or falls away, Bill and Virginia find solace in one another. Series finale.
