Rich Sommer Rich Sommer

It's going to be a busy weekend for Mad Men star Rich Sommer.

Before the AMC drama wraps up its third season Sunday night (10/9c), Sommer will appear in a ripped-from-the-headlines episode of Law & Order (Friday at 9/8c on NBC). "The episode is sort of inspired by the woman who drove the wrong way down the Taconic [Expressway]," Sommer tells "I play her boss, and after some investigating, they begin to suspect him a little bit, that somehow he may have been involved."

Check out photos of the Law & Order cast

Although the role sounds significantly darker than Harry Crane, the baby-faced nice guy he plays on Mad Men

, Sommer says the two characters have more in common that one might expect. "This guy is not actually that far off [from Harry Crane]," Sommer says. "Harry's very ambitious and so is this guy. And I think if Harry let his ambitions get the better of him, enough to cloud his judgment, he could end up being this guy. It's only a few degrees off — he's still a nice guy, but it will be interesting to see how it plays."Harry's judgment has been a little off this season on Mad Men. When one of Sterling Cooper's biggest clients' come-ons were turned down by closeted art director Sal (Bryan Batt), the client asked Harry to remove Sal from the campaign. Even though Harry's inaction led to Sal being fired, Sommer says his character had no choice.

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"He was screwed either way," Sommer says. "Whether he called Roger then, or Roger found out the way he found out, Roger still would have said, 'Why the hell was he calling you?' It wasn't Harry's fault. The only thing he did was work late and pick up the phone, but it's still going to come back to him because blame has to be put somewhere. He could have called, but since he's screwed either way, I think it was worth rolling the dice and hoping it would just go away."Sommer also took part in one of this season's most shocking and lasting images: Harry and a group of onlookers being splattered with blood when a drunken secretary runs over a visiting exec's foot with a riding lawn mower. Sommer says he wasn't quite sure about the scene when he read it on paper."I was the first one to question how it was going to fit in the show. I didn't really understand it," Sommer says. "I do that all the time, and then, of course, it's weaved in beautifully somehow. So I remember just being like, 'What the hell is going on? Are we jumping the shark? Is the new term "mowing the foot"?' I was nervous, but it turned out shockingly and beautifully. They know what they're doing; I should trust them more."

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That scene seems so long ago, now that we know how the men and women of Mad Men experienced the assassination of President John F. Kennedy. Sommer says the episode was tough to watch. "Seeing it all put together, it made me feel sick a little bit," Sommer says. "My only moment that I can compare to that is obviously 9/11, and watching that episode, I felt almost like I did watching United 93. There's just that feeling of watching people go from innocent to knowing. That was the hardest part of the movie for me, and you get that in the show. You see all these people floating around, and then all of a sudden it's crystallized and it's painful."Naturally, Sommer was tight-lipped about the top-secret season finale, but he says it's an appropriate closing to this chapter of the show. "I think this has been our best season yet, and I think that the finale holds up in that way," he says. "It's going to be big. It answers questions, and it asks plenty more. It's a good one. We've said from the beginning that this season was about change, and I think that carries through up through this finale."