Howard's idea of cleaning up in preparation for a dinner party at their place is to throw everything into the closet, which irks Bernadette. Howard suggests that if Bernadette truly wants their closet to be organized, that they show it to Sheldon, who will more than gladly volunteer to organize it, which he does. But Sheldon finds something in the closet that Howard has kept unopened for years: a letter from his father, who abandoned him and his mother when Howard was a child. The letter arrived on his eighteenth birthday. At the time, Howard had no interest in reading the letter's contents, but now doesn't know what to feel about it. Regardless of what Howard decides to do about the letter, he and others may find out its contents if only because Sheldon read the letter in deciding how to file it. A scientific experiment may reveal or not reveal the letter's contents to Howard. Meanwhile, Leonard, seeing how grown up and mature Howard and Bernadette have become by hosting a formal dinner party, wants him and Penny to do the same, but only better.