When Masters of Sex returns, it's 1966 and the Sexual Revolution is in full swing (so to speak). Bill Masters' (Michael Sheen) wife Libby (Caitlin Fitzgerald) has not only accepted her husband's infidelity with his sexual research partner Virgina Johnson (Lizzy Caplan), but even views her as a friend. Bill and Virginia are on the brink of publishing their groundbreaking first book, Human Sexual Response, and any hint at loose morals could undermine their efforts.