Ep 6. The Middle Earth Paradigm

Leonard, Sheldon, Howard, and Raj are heading out to a Halloween costume party, and each of them is determined to make an impression. Leonard has his sights set on Penny, and he's hoping that his Frodo Baggins costume will help him make a good impression on her. Sheldon, ever the perfectionist, has gone all out, opting to dress as the Doppler Effect, a costume that has him handing out glow sticks to partygoers to demonstrate the idea of red and blue shifts. Not to be outdone, Howard has chosen to dress as Robin Hood, complete with a fringe-trimmed cape, a bow and arrow, and a pair of tight, green tights. Last but not least, Raj, who can't even speak to women without the aid of alcohol, chooses to go as a vampire, complete with fake teeth and a cape.

Unsurprisingly, the guys' costumes fail to impress their female counterparts, who opt for more sedate costumes such as a cat, a cheerleader, and a cute, fuzzy bunny. The four men find themselves feeling awkward and out of place as they attempt to navigate the party, with Leonard in particular struggling to make a connection with Penny. Matters are made worse when Raj accidentally spills his drink down Penny's costume, forcing her to take drastic action in order to avoid being seen in public.

Back at the apartment, the guys are still reeling from the embarrassment of the party when they receive a group text from Penny. She invites them over to hang out, and Leonard is convinced that this is his chance to make a move on her. However, things don't quite go according to plan as the guys can't resist slipping back into character, with Sheldon in particular still obsessing over the Doppler Effect. In the end, Penny manages to get through to them and they all have a good laugh about the events of the night.

Despite the lack of success with their costumes, the guys learn a valuable lesson about the importance of being true to oneself. As Leonard puts it, "A good costume should be about expressing something you can't normally express." In the end, he manages to win Penny over by taking off his Frodo costume and revealing his true self. The episode ends on a positive note, with the group hanging out and enjoying each other's company, sans costumes.