The Beach Girls is a story about a nerdy girl whose uncle allows her and two friends to stay at his beach house. The two friends decide to throw a party and start by ordering a pizza from the phone book. As the night progresses, they call various service people and soon the house is filled with people, making the party loud and wild.
The caretaker tries to spy on them, prompting the next door neighbor to call the police. Surprisingly, the officer joins in on the fun. When one of the friends calls a liquor store for booze delivery, they accidentally reach the uncle's fiance, who approves the order. The uncle, concerned about the situation, decides to drive out to the house.
Meanwhile, a boat smuggling marijuana is forced to drop its load while being pursued by the Coast Guard. As the uncle arrives at the house and plans to ask the people to leave in the morning, the two friends seduce him into agreeing to another party that night. The neighbor informs the fiance, who arrives at the house with her chauffeur.
The Coast Guard, after capturing the smuggler, plans a raid on the house that evening. However, the two friends had found the marijuana bags on the beach and decided to distribute them at the party. As chaos ensues, the fiance joins the party after being handed a joint.
Finally, the Coast Guard raids the house and burns the marijuana on the beach, causing everyone to inhale the smoke and act silly.