Quagmire babysits Meg, Chris, and Stewie while Peter accompaniesLois on a visit to her pregnant, newly single sister, Carol Pewterschmidt. When Carol goes into labor, Peter drives her to the hospital (stopping to get drive-thru on the way). Carol's obstetrician,Dr. Hartman mistakenly jabs himself with several used needles, and faints, leaving Peter to deliver the baby himself. Revealing that the baby is a boy (Peter thought it was a girl with a penis). Reminded of the experience of childbirth, Peter tells Lois that he wants to have another child. Lois gleefully tells the rest of the family, but Stewie feels threatened in his position as the youngest and resolves to prevent the conception of another sibling.
Stewie attempts to interfere in a romantic moment by crying for attention. Foiled in this effort, he smears one of Peter's shirt collars with lipstick but Lois catches him when he gets distracted by his own image in the mirror. In another attempt, he chloroforms Peter and utilizes a mechanical replica of him to insult Lois, but Chris and Megaccidentally knock him out the window, where Stewie jumps out in front of Cleveland, much to Cleveland's surprise. When a candlelit dinner threatens to lead to intimacy between his parents, Stewie shrinks himself and a spaceship-like vessel and enters Peter's body to destroy his sperm.
In his well armed craft, Stewie easily slaughters the defenseless sperm with one exception: Bertram, who seems to be just as diabolically clever as Stewie himself. After a brief struggle and standoff, they are both knocked out. Stewie recovers first, and has Bertram at knifepoint, before he realizes that they have much in common, that they both want to kill Lois. Bertram claims to be the twinkle in Peter's eye. Additionally, with Bertram's help, he could accomplish many goals, including Lois' murder. They part on amicable terms, Stewie thinking it will be easy for Bertram to escape due to most of the sperm being killed, but Stewie has only moments before the ship reverts to its normal size. After a narrow escape through Peter's tear duct, Stewie steers the craft back to his room with no time to spare.
Peter and Lois, however, reconsider having another child, to Stewie's chagrin. He frantically tries to get her and Peter to resume their plans ("You must receive his seed!"), but Peter retreats to the bathroom andmasturbates with the assistance of a lingerie catalogue. Stewie, appalled at Bertram's apparent death, despairs until he notices a twinkle in Peter's eye signifying that Bertram is still alive. His relief is only momentary as he realizes that his unborn brother may be tooclever.