revised:

“So, Garry, what have you got to show me...” Professor Jeff Pullman glanced at his watch, "...at this time of night?" He couldn’t believe it--they had to be at the University’s annual dinner soon and his wife had let this ex-student in their home.
He glanced at Lorraine, who was uncharacteristically wringing her hands. Why did she let him in?
He watched Garry as he pulled small bits of equipment out of his briefcase and laid them on the hall table. Good-looking lad--he probably just smiled sweetly to her.
“Well, sir. It's based on a device you created--and patented--which is why you need to see it first.” Garry Lebow flashed his white teeth. “Of course, I've modified what you created and added significant value to it.” Another smile.

Revised:

“So, Garry, what have you got to show me at this time of night?” Professor Jeff Pullman glanced at his watch. He didn't understand it--they had to be at the University’s annual dinner soon and his wife had let this ex-student in their home.
He glanced at Lorraine, who was uncharacteristically wringing her hands. What was she thinking?
He waited as Garry pulled small bits of technical equipment from his briefcase and laid them on the hall table. He's a good-looking lad--probably just needed to smile sweetly at her.
“Well, sir. It's based on a device you created--and patented--which is why you need to see it first.” Garry Lebow flashed his white teeth. “Of course, I've modified what you created and added significant value to it.” Another smile.

[This message has been edited by Kathleen Dalton Woodbury (edited September 18, 2008).]

Only 2 things that bothered me, neither of any real significance

1. the first sentence feels a bit choppy. I dont see anything wrong with it (maybe needs a question mark somewhere? but who cares.) I think its the "..Jeff Pullman glanced at his watch,"...at this time of night."" It kind of runs together or something. I thinks it's the "at"'s that are throwing me off. Sorry can't be clearer on the matter but thought I should point it out.

2. His thought - "Good-looking lad—he probably smiled sweetly to her and she let him in." Takes me out of the story. I feel like its an abrupt switch of focus from Garry- and the things unfolding in the story- to Jeff's wife being a sucker for a pretty face.
I think the "Why did she let him in?" is sufficient. its short and comes across as a quick, passing thought for a man who is in a hurry. If it turns out that he is still bothered at the fact that his wife let Garry in maybe have him ask her about it once they are in the car on their way to the dinner. ("why the hell did you let him in anyway Lorraine?" "well dear, he said he managed to complete that flux capacitor youve been working on for years. i thought you'd want to see it immediately")

If the point is to get across the fact that Garry is a good looking lad id suggest adding it to the line "Garry Lebow flashed his white teeth, working his boyish charm"

With the way the first sentence is split up, I wasn't sure who the "He" was in the second sentence at first. I was putting myself in the role of Garry as MC until you mentioned the dinner. Prob the only one who read it like that, though.

I'm intrigued by the ex-student but I don't feel the professor's reaction. Is it a student he was fond of? A troublemaker? I think if you emphasize a previous frictional relationship I'll understand the professor's disbelief even more. Also, the improvement of his invention will be more of a challenge/threat.

I don't think you need the internal question. He's already expressed confusion/disbelief in the first paragraph. Because you mention the uncharacteristic hand-wringing, I'm expecting the professor to be wondering about that, perhaps asking, What had Lorraine so upset?

Good mix of action and dialogue. Everything is flowing smoothly.

I think I would have liked a little more description of the device, but that might just be me.

I actually like the original version of the first sentence better.