When Penny and Leonard try to get out of beta testing Sheldon's board game he created, Penny casually slips she can't play next Saturday because she's picking up an old friend... she used to date... from the airport to crash on her couch for a couple weeks.  Woh, so not cool.  Leonard and Penny have the pretty standard couple fight with lots of screaming that reminds Sheldon of his parents fighting back in Texas.  

Sheldon can't handle it and attempts to reunite the couple by heading to Cheesecake Factory and begging Penny to apologize and when that fails asks Leonard to.  When all that fails, he just heads to the comic book store to hide like a child.  Penny and Leonard go to pick him up and act exactly like parents and buy him a toy robot and comic book.  In the end, Penny's friend ends up crashing on Leonard's couch and everyone is happy, except Sheldon.

Meanwhile, Raj and Wolowitz have yet another lover's quarrel over Wolowitz again ditching him.  Raj seems to realize what his relationship is becoming and agrees to go to India to be set up with a woman at a wedding.  We'll see if that actually comes into the storyline again.