In part 1 of "NERD Throws PARTY Behind Parents' Back," Nelson learns that his parents will be out of town for New Year's, prompting his friends to suggest throwing a party at his house. Although he's hesitant, he ultimately agrees, hoping to impress Shannon, the girl he likes. As the preparations begin, he struggles with peer pressure and the challenge of managing the party.

Despite warnings from his friend Arthur, Nelson finds himself swept up in the excitement, facing a series of questionable decisions as more guests arrive, including a few from the school's popular crowd. Tensions rise as Nelson tries to maintain control over the chaos while navigating his feelings for Shannon, who seems more interested in using him for the party than genuinely liking him.

As midnight approaches, the atmosphere becomes increasingly reckless, and Nelson's efforts to keep things in check falter. The pressure from his friends culminates in him taking a shot, setting the stage for a wild night. The episode ends with a cliffhanger as Nelson's parents unexpectedly decide to return home early, leaving him scrambling to cover up the mess before they arrive.