Season synopsis
Contains spoilers for this season and earlier seasons.
The season opens after Leonard and Penny's first date. Penny confides in Sheldon that she lied about finishing community college because she feels uncomfortable beside Leonard's education. Sheldon struggles to keep her confidence and briefly moves out rather than hide the secret from Leonard. Once Leonard learns the truth, he gives Penny college brochures and offends her. Their awkward attempt at romance gives way to friendship, while Leonard dates other people and Penny's feelings remain unresolved.
Sheldon is gradually drawn into Penny's orbit. Her Christmas present, a napkin signed by Leonard Nimoy, delights him because it gives him Spock's DNA, and he responds by giving her a hug. Raj makes a professional breakthrough when he identifies a trans-Neptunian object, then later manages a brief apology to Penny without alcohol. Howard's short-lived relationship with Leslie Winkle exposes a more vulnerable side beneath his usual pursuit of women. Work, friendship and social habits keep moving alongside Leonard and Penny's unresolved feelings.
In the finale, Sheldon's work on magnetic monopoles earns him the chance to lead research at the North Pole. He asks Leonard, Howard and Raj to serve as his support team for three months; after weighing the strain of working under Sheldon against the scientific opportunity, they agree. Penny learns how long Leonard will be away and gives him a Snuggie, then says she will miss him. Leonard cannot tell whether she means anything more, but after she closes her door she admits she wishes he were not going. The group leaves for the Arctic with the relationship still undefined.