O estudo se expande para a inclusão de casais, o que faz com que Masters e Johnson descubram que a ciência do sexo se complica com os mistérios da atração. Enquanto Johnson tenta se reaproximar do filho, Masters experimenta a ansiedade de se tornar pai. Para completar, Ethan pode ter problemas com sua carreira médica.

Masters e Johnson acreditam que é preciso filmagem para conseguir o melhor resultado no estudo, mas para isso eles precisarão de ajuda de fora. Johnson retoma os estudos e vê obstáculos no caminho, enquanto Haas e Langham falam sobre os méritos do casamento.

Masters deals with the ramifications of his disastrous presentation and being fired from the hospital. Meanwhile, Libby urges Masters to get another job; and Virginia fights off advances and innuendos stemming from the belief that she was the woman in Master's explicit film.

Masters begins a new job at Memorial Hospital under Betty's extortion terms only to discover that his boss insists he leave Virginia behind in favor of a handpicked secretary. Meanwhile, Johnson is torn between pressing Masters to rehire her and staying by DePaul's side as her condition worsens.

Masters delivers a baby with ambiguous genitalia and urges the parents not to surgically assign the child a sex out of fear or convenience. Meeting Virginia at a hotel for a secret rendezvous, the two of them divide their attention between sexual role-play and a championship boxing match, prompting Virginia to unearth the truth of Masters'' troubled childhood.

Masters privately treats a couple for infertility, without revealing his relationship to them. Johnson realizes her work with Masters can be used to help people suffering from sexual dysfunction - but quickly gets in over her head when she attempts to treat Barbara Sanderson on her own. Libby is unnerved after witnessing a hate crime that is then whitewashed by the police.

Masters and Johnson find their life's work in jeopardy. Season finale.

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 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. Season finale.