Sheldon is angry at Penny because she bought him a Christmas gift. Sheldon now feels he has to reciprocate and go through the trouble of buying something for someone he doesn't really understand, all at the same price of the gift he is about to receive. Meanwhile, David Underhill, last year's MacArthur grant award winner based on his work which has basically rendered Leonard's recent work meaningless, is a new addition to the Physics department at Cal Tech. Regardless, Leonard is enthralled to be working with Dave, who is not only good looking, but Leonard learns is a Renaissance man. Upon their meeting, Dave is attracted to Penny, and vice versa, and they decide to date. Penny even pretends to be a science geek to impress him. Leonard is angry at Penny's hypocrisy, since she was scared that Leonard was too smart for her to date. Penny, however, has some more important news about her relationship with Dave.