One day, in the local library, he encounters Laura, a new librarian. Fascinated by her good looks and driven by, as he sees it, sinful desire, he is for once able to overcome his shyness and asks her out. Laura accepts, they immediately fall in love with each other and start dating on a regular basis. However, he prefers not to tell his possessive mother about her let alone invite her home.
In the course of the following weeks Vincent's life is shattered by a number of revelations concerning Laura. He is disappointed when she tells him that she is a Protestant and that, on top of that, she has stopped going to church altogether. What is more, through a deliberate indiscretion by Laura's flatmate Ruth, he learns that Laura is divorced. For him as a Catholic, this means that he is seeing a married woman, and both his guilt and his helplessness about the situation increase enormously. Accordingly, they break up their relationship.
Surprisingly, soon afterwards Vincent loses his virginity with Maureen, his sister-in-law, while his brother Matthew has gone out and the children are asleep. On the following morning, back at his mother's, he recollects what happened the previous evening:
[…] He had deliberately denied himself the one pleasure that had the power to transform his very notion of pleasure; he had committed all the other sins because of indolence or indifference, never stopping to calculate the price. He smiled; it was the same for the sin you enjoyed as the sin that you didn't.
To spend the day talking to schoolboys about James I was, he reflected over his scrambled eggs, an anticlimax […]. He smiled to himself: if he had been a savage he'd have been entitled to wear some special insignia […].
"I'm glad you're so cheerful," his mother said.
"It was something in the Guardian," he said.
That very day, Vincent has an appointment with a senior clergyman about his vocation and once and for all makes up his mind not to become a priest. He also decides to see Laura again. In the meantime she has settled down in a flat of her own, and this is where they have sex for the first time, without Vincent confessing to Laura that he has recently made love to his own sister-in-law. When, some weeks later, Maureen announces that she is pregnant again, he is of course afraid that he might be the father of her baby. Out of jealousy, Maureen writes Laura's ex-husband Robert an anonymous letter, urging him to make up with his wife again. Vincent and Laura split up again as Laura is not certain about her husband's intentions.
In the end two instances of deus ex machina resolve the complicated situation. First, Maureen has a miscarriage, freeing Vincent of any doubt that he might have fathered an illegitimate child. Then Robert commits suicide, paving the way for a Catholic wedding between Vincent and Laura, who are planning to leave the past behind and start a new life somewhere else.