Plot

When Meg turns 18, Quagmire tries to make his move on her, but Peter tries to stop him.

When Meg finally turns 18, Quagmire seizes the opportunity to pursue his next romantic conquest. As the new couple's relationship blossoms, Peter stops at nothing to come in between his innocent - well, somewhat innocent - daughter and his creepy friend.—Fox Publicity

When the family plans a surprise party for Meg's 18th birthday, the only person to show up is Quagmire but his intentions to seduce Meg become quite clear. However, when he leaves without incident Peter lets it pass. Quagmire continues to flirt with Meg and talks her into going out with him. When Quagmire shows up for their date, Peter objects but Lois allows her to go out with him, telling Peter it's just a ploy for attention and she'll rebel if they try to stop her as Lois herself did against her father. After their date where Glenn fails to score but considers it just a temporary setback, he arrives in his home to find Peter waiting for him. Peter orders him to stay away from Meg but Quagmire points out that she's 18, legal and ripe for the picking and Peter vows to stop him.

As Quagmire continues his attempts to get into Meg's pants, Peter manages to keep them separated. Peter tries to talk some sense into Meg but she complains to Lois who tells Peter again not to push her into rebelling. Lois changes her tune when she finds out later that Meg and Quagmire went off to his sex cabin to be alone and she and Peter set off to stop them, admitting that Peter was right not to allow Quagmire to have a free shot with Meg. They arrive as Meg and Quagmire are in their underwear and Peter orders Meg to the car. She tries to stand up to Peter pointing out she is 18, but Peter states that he is still Meg's father no matter what age she is and puts his foot down. As for Quagmire, Lois confronts him and threatens to cut his "thing" off and feed it to Brian. She also demands use of his cabin once a month for her and Peter.

Back at home the next morning, Meg thanks her parents for not allowing her to make a mistake with Glenn and Peter recalls making his own mistake sexually with an older woman when he was 18.