This season, Jessica Pare, as Megan Draper, has delivered some of the best moments in this or any season of Mad Men. She sang seductively to husband Don, in French, at a party that left him mortified and angry. When he was angered, again, by her dislike of the orange sherbet at Howard Johnson’s, she sarcastically shoveled spoonfuls of it it into her mouth like Harold defiantly ate his beets in Harold and Maude. Then, last week, after Don and company talked about hiring a group that sounded like the Beatles for a new TV spot, Megan brought home the real deal: a copy of the Revolver LP. And she told him to go straight to “Tomorrow Never Knows,” a song so far ahead of its time that it sounds futuristic even now. As Don listened to the song, he confronted something inexplicably, uncomfortably new. The theme, it’s clear already, for this mid-Sixties season of Mad Men. Even the song title fits the show’s theme perfectly.