Season 4 ends with Masters and Johnson working to save the practice from disintegrating in the face of insurrection within the clinic. Meanwhile, Bill and Virginia find solace in one another as everyone in their lives either moves on or falls away.
Masters and Johnson return from Topeka and grapple with the trip's ramifications. Meanwhile, 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 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 looks to groom Art as his protégé in a new area of research, while Johnson does her best to keep Nancy at arm's length. Elsewhere, Betty seeks an unlikely source to assist in her fight for equal rights to Helen's baby.
Johnson looks to get her relationship with Masters back on track, but Masters does his best to find satisfaction elsewhere. Meanwhile, Betty and Helen ready themselves for a new addition; and Art and Nancy discuss the consequences of their party.
Johnson and Masters' legal troubles come to a head as the trial begins with Keller leading the charge. Johnson, assuming they're to be exonerated, does her best to revive their careers, while Masters faces the reality of what these charges could mean for him, Johnson and the practice.
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 previous evening.
Masters and Johnson adjust to new partners, but their respective cases cause them to second-guess the instinct to remain separated. Meanwhile, a romantic prospect pushes Libby to embrace life as a newly single woman of the sexual revolution.
Season 4 begins with Masters and Johnson searching for purpose after their fallout and looking to work to save them as their personal lives crash down around them. Meanwhile, Libby finds herself alone for the first time and discovers some unexpected allies.