Sheldon Cooper's eccentricities form the basis of many episodes of "The Big Bang Theory." At first, "The 43 Peculiarity" follows that familiar pattern, but producer Chuck Lorre throws one heck of a curve ball during the closing minutes of the episode.
Howard (Simon Helberg) and Raj (Kunal Nayyar) notice that Sheldon (Jim Parsons) disappears for 20 minutes each day between 2:45 p.m. and 3:05 p.m. To solve the mystery, they follow him to an out-of-the-way room on the Caltech campus, but they can't hear or see inside.
Frustrated, Howard and Raj return to campus late one night to pick the lock on the door of the mysterious room. Inside, they find discarded equipment and a blackboard with the number 43 written on it. The two brains spend hours attempting to decipher those digits but without any concrete results.
As that mystery deepens, Leonard (Johnny Galecki) feels insecure when Penny (Kaley Cuoco) receives texts from a male classmate. Leonard panics when he hears they will be working on an oral report at her apartment. The physicist almost loses it when he hears her friend has an English accent.
Leonard tries to spy on his girlfriend and her male friend through the peephole of his apartment door. At one point, Leonard follows him down the stairs, telling the hapless student that Penny's boyfriend is a pretty scary dude and runs with a gang called "The Scientists." Penny overhears what he's saying and definitely is not amused.
Back at the university, Howard appropriates a spare camera for the Mars Rover to spy on Sheldon. The shocking video feed shows the theoretical physicist opening a wormhole into another dimension. He has checked out 43 worlds thus far, hence the number on the blackboard. His latest attempt, however, appears to unleash a dangerous creature.
As it turns out, Sheldon spotted the hidden camera early on and fed a bogus video stream to Howard's laptop. He finally explains that for 20 minutes each day, he shuts his brain down to relax and recharge in private. The closing gag of the episode shows that Sheldon uses that downtime to play hacky sack (the 43 represents his personal best in the game).
In the cafeteria, Leonard shares a coffee with Alex (Margo Harshman), Sheldon's cute assistant. Blinded by his situation with Penny, Leonard can't tell that Alex is hitting on him -- even when she practically says how much she likes him.
Back home, Leonard and Penny finally talk in the hallway about his jealousy. In the biggest surprise of the season thus far, Penny reassures her boyfriend that she loves him. It takes a few seconds for the couple to realize that this is the first time she said those words. It's a revelation that brings both of them to the verge of tears.
"The 43 Peculiarity" starts out as a typical episode, but that hallway moment is the highlight of the episode. Kaley Cuoco and Johnny Galecki handle Penny's revelation beautifully. The L-word was the original reason the couple broke up at the end of Season 3. Without fanfare or flowers, Penny says it quietly and from the heart to Leonard.
Based on Alex's obvious affection for Leonard, there still may be romantic trouble on the horizon for this "Big Bang Theory" couple.