John Slattery John Slattery

"Who is Don Draper?" was the opening line of Mad Men this season. As it concludes, will dapper Don (Jon Hamm) be any closer to the answer? "Absolutely, conclusively," insists John Slattery, who plays fellow adman Roger Sterling. "Don came through his divorce, started the new business and survived his own personal cauldron. He ends the year transformed."

Beyond that, Slattery can't say much; Mad Men types tend not to gossip. But much is to be resolved by season's end: Don's secret past may or may not be his undoing. Will there be lingering effects from Roger's hookup with sultry office manager Joan (Christina Hendricks)? And what about breakout character Sally Draper, whose existential crisis has rivaled that of her dad's? "She's a girl with the soul of an adult," Slattery says of 10-year-old Kiernan Shipka.

Slattery isn't spilling the beans, but he says the clues are all there. "If you look back at the episodes this season, all the threads are leading to answers," he says. "There are no surprises. Just pieces of the puzzle falling brilliantly into place." Come on, John. Not even a hint? "OK, keep an eye on Peggy," he says, referring to Elisabeth Moss' character, who's evolved from eager-beaver partner to feminist this season. "She represents the future. The changing world is reflected in her eyes."

Mad Men airs Sunday at 10/9c on AMC.

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