Yes, that's Jon Hamm as Don Draper, sitting in his office in several inches of water. And it's no special effect: as revealed in the video after the jump, it's a whole set filled with actual water — which at one point reached up to Hamm's neck.
The theme of this season is meant to be change, and this poster image is the one that beat out a pile of other high-concept ideas (Don Draper on an ice floe? Don Draper getting sucked into a whirling black hole?). That said, the image — and the show's new tagline, "The World's Gone Mad" — don't reveal a whole lot of details about the new season. But they sure do give us a good jumping-off point for speculation.
So, let's speculate! Why is Don Draper drowning? To discuss, and check out the making-of-the-poster video, just read more.