Showtime’s historical drama about the duo who pioneered research into human sexual responses has a pair of new faces for Season 4 arcs. Niecy Nash will play an Alcoholics Anonymous veteran and Betty Gilpin is joining the practice of William Masters (Michael Sheen).

Showtime

The next season of Masters Of Sex, which also stars Lizzy Caplan, will begin in 1968 and take viewers into the “swinging ’70s,” during which time the characters will take on new partners both professionally, personally and sexually. Nash will play Louise Bell, a local AA chairperson running Masters’ court-ordered daily meetings. She fervently believes in AA’s message, and uses it to push Masters to reevaluate his life. Gilpin will play Nancy, a former medical student of Barton’s (Beau Bridges) who partners with Masters, adding a second MD to the practice.

Production on Season 4 is underway in Los Angeles for a September 11 premiere. Caitlin FitzGerald and Annaleigh Ashford also star. The series from Sony TV is executive produced by Michelle Ashford, Sarah Timberman, Carl Beverly, Amy Lippman and Judith Verno.