He happily gets back into his routine by going on his combined run and shopping expedition. On his way, he reflects on the events of the previous day. Don is thrilled to have gotten Rosie’s telephone number, even if it is only for business purposes. He knows this is a common occurrence between men and women, but as it had never happened to him before, he assumed it never would. While he knows Rosie gave him her contact information so they could further discuss the Father Project, he fears that she may decide she made a mistake. 

Don notes that because he is a regular customer who always buys the same ingredients on his grocery days, the shop keepers at each stall in the market usually have his purchases ready to go. He only needs to pause in his run to pay. On the way home, Don continues contemplating his interest in the Father Project. He decides his reason for helping her came more from illogical instinct, so he calls Rosie with the intent of revoking his offer. He leaves a message, and she calls back while he is giving a lecture. Because he answers the phone in front of his students, he is unable to tell her that he wants to back out. So, when she accepts his offer, he believes he is morally obligated to help after all. Rosie thanks him by saying “You’re a star” (77), which he does not initially understand. He blurts out that he likes her, which causes his students to break into applause, as they interpret this as a romantic expression.

When they meet for coffee the next day, they agree to collect the DNA samples together. She has a local candidate picked out, Dr. Eamonn Hughes, who she believes is her father because he was a constant presence in her life as she grew up. They go to Dr. Eamonn Hughes’s house on Saturday, planning to gather his DNA from a coffee cup. However, they run into a snag because Eamonn’s wife accompanies Rosie to the kitchen, where the latter had planned to collect the sample while cleaning up. So, Don comes up with a ruse about a genealogical study where people’s ancestry is determined by analyzing their DNA. Eamonn is intrigued, so he willingly gives them a blood sample. 

At the lab where Don will test the DNA, he feels an unusual disappointment that the room is not more impressive—implying he wants to impress Rosie, though he is not sure why. Rosie babbles nervously as the test is running, and when it is done, the sample proves Eamonn is not her father. The pair goes out for a drink to help Rosie recover from her disappointment. While Rosie leaves to take a cigarette break, Don sees Gene with Olivia—the woman he met at the group dinner date—leaving the restaurant. When a passing waiter asks if Don and Rosie would like to occupy the table Gene and Olivia had just vacated, Don agrees on instinct. Rosie and Don end up having dinner and once again enjoy each other’s company. Rosie tries to explain to Don why it’s so important for her to find her biological father because he feels it is impractical now that she is already grown and could test her own blood if she was worried about any inherited conditions. Still, he knows that it’s important for her happiness. When Rosie goes to the restroom, Don attributes this unaccustomed social success and his happy feelings to the fact that he’s already eliminated Rosie from consideration as a partner. After she returns, he asks Rosie who they are going to test next.

Rosie knows of two other close family friends from her mother’s graduation class: Drs. Peter Enticott and Alan McPhee. Dr. Enticott lives locally, but since Dr. McPhee is dead, they decide to collect a sample from his daughter, Natalie, whom Rosie knows socially.

Before collecting their samples, Don has another uncomfortable discussion with the dean; a medical student has come forward saying Don tried to humiliate him in class. The student in question had taken Don’s class the previous semester and brought up “creation science” (87) to point out that evolution is simply a theory. While Don knows this is technically true, he believes that evolution is unequivocally true. As a result, he presents the student with a flounder to demonstrate evolution; his argument is that the fish’s asymmetrical eye placement proves it was not created by an “intelligent designer” (88). Though Don technically did not broke any rules during this interaction, as usual, his actions are against social convention. The dean tells him that he must try harder to “fit in” (89), which terrifies Don. He knows that if he, a scientist, cannot fit in successfully with the science faculty, he cannot fit in anywhere. As he leaves the office, the dean’s assistant reminds Don that he has not bought tickets for the upcoming faculty ball.

Rosie drives Don to Natalie’s house in her stepfather’s red Porsche. Don is surprised because he was under the impression, based on Rosie’s anecdotes, that Phil was not fond of his stepdaughter. But Rosie says Phil always gave her material objects in lieu of love. At Natalie’s house, the plan to gather DNA from a coffee cup goes awry once again. Don decides getting a sample from Natalie’s newborn would be acceptable, but Natalie refuses to leave him alone with her baby. Rosie and Don leave when the baby wakes up, and Rosie reveals she took hair and Natalie’s toothbrush while she was using the restroom. Rather than test this sample immediately, Rosie says she wants to get the final sample first. Don thinks this is illogical because Natalie’s DNA might prove Dr. McPhee was Rosie’s father, rendering the third sample unnecessary. But he agrees. 

They meet with Peter Enticott on the pretext of talking about Rosie’s application to the medical school where he teaches. Don is surprised that this was the plan Rosie came up with; her job as a bartender does not, in his view, suggest she has the intelligence needed to be a doctor. So, the fact that Dr. Enticott does not question her story is even more surprising to Don. The waiter takes the cup Dr. Enticott was drinking from as he drops off the bill, so Don follows him to the busing cart. Rosie creates a distraction so he can retrieve the cup. Don is appalled to learn that her distraction was running out without paying, and he wonders, “What [is] happening to me?” (94) as they drive away.

On the way back from the meeting with Dr. Enticott, Rosie takes a detour to the beach so she can clear her head. The deviation from his schedule sends Don into one of his panics, but he respects the way Rosie wants to deal with her feelings before running the tests. After walking on the beach, they resume their drive home, and Rosie plays “Satisfaction” by the Rolling Stones because Don mentioned his father used to listen to classic rock. This burst of nostalgia leads Don to again experience happiness and contentment in Rosie’s company; he reflects that he is temporarily entering a world that was once inaccessible.

At the lab, Don compliments how well Rosie sold her phony story about applying to medical school—particularly that Dr. Enticott believed her when she said she scored exceptionally well on the entrance exam. Rosie challenges Don’s prejudiced view of her, arguing that because both her parents were doctors, it stands to reason that she is capable of the same. Don knows she is right and realizes he likely has many unfounded prejudices because he formed all his opinions based on TV and movie characters, rather than actual human interaction. 

When tested, neither of the DNA samples matches Rosie. She is very discouraged and sad, and she brushes off Don’s protests about solving the problem after she says they have reached the end of the project. Don thinks about the irrationality of human behavior, specifically how people ignore more pressing matters to focus on trivial things. He notes that he is capable of this irrationality as well because instinct often overpowers reasoning; his proof is the fact that he still cares about the Father Project. Over a bottle of wine, Don again tries to convince Rosie that they should press on. But she makes the point that finding and testing all the remaining men in her mother’s graduating class would be too big of a task. He knows she is right, but he still wants to think it over.