The Seducer's Diary commences with an introduction by A, an invention of Kierkegaard's who is the author of the works comprising the first half of Either/Or. His essays and miscellaneous writings controversially praise the value of living in a purely aesthetic sphere of existence. Yet even he finds the impassioned deviousness of the seducer, Johannes, to be too much. While A's pieces in Either/Or examine seduction, amibiguity, and melancholy in a favorable light, he is nonetheless disquieted by Johannes peculiar Diary and his poeticized abandonment of Cordelia. This may be particularly true because A mentions that he believes he once knew this Cordelia—though he is not particularly certain of this fact, as the Diary is shadowy in true details.
For the same reason, his presentation of the diary is haphazardly organized at best:
“It is true that the dates are lacking, but even if I had them it would not help much, since the Diary as it progresses becomes more and more sparing of dates, until at last it is a marked exception when one is given, as if the story in its progress becomes qualitatively significant to such a degree that, although historically real, it comes nearer to being idea, and for this reason the time-designations become a matter of indifference.” (306-307)
The first materials A reveals to us are three letter-notes by Cordelia herself, the seduced. The first letter is accusatory, bitterly acknowledging that she never possesed Johannes the way he possessed her. The second letter is similar in intent, though it is more obscure in that she draws mainly from an anecdote about a rich man who took from a poor maiden her single lamb. The third letter is despairing, yet it reveals that she still has hope that Johannes may someday love her truly. A includes the letters to give us an idea of how Johannes has manipulated Cordelia so far as to leave her emotions muddled and her convictions uncertain.
The rest of the work is the diary itself; in the first entries, very little actually occurs. The journal begins in the spring, with his description of his first glimpse of Cordelia, stepping out of a carriage, and his thoughts on how beautifully exploitable and to his advantage the world is, simply by nature. The majority of the following entries are similar. As Johannes stalks her, he jots down disturbing analyses of every move Cordelia makes, detailing his rationale for not advancing too quickly: so that he may savor the ideal of the pursuit of her.
Soon enough, he discovers her name, that she lives near the ramparts, and that she has no family other than two sisters and an aunt. Johannes decides that the way into the household will be to win the favor of the aunt, and he does so facilely with his charm.
However, to get closer still to Cordelia, he befriends a young man named Edward who is enamored of Cordelia, but uncertain about how to go about courting her. Johannes wins his trust and becomes his confidant, encouraging him to try to woo Cordelia only to eventually have him fall and lose her interest. He circulates a rumor that he is in love with a young girl, which subtly makes its way to Cordelia through Edward, making him an unwitting conspirator. As he struggles to decide when to terminate their relationship, Johannes meanwhile also attempts to find the most aesthetically pleasing and practicable way to surprise Cordelia.
He to propose to her one day while Edward is away and only she and her aunt are at home. Without being overly effusive, rather talking like a book—"for a book has the remarkable quality that you may interpret it as you wish"—he gives his petition. Cordelia says neither yes nor no, but refers him to her aunt, who gives Johannes her consent.
As soon as they are engaged, Johannes schemes to have her question their engagement. In becoming distant and allowing Cordelia to "triumph in pursuing" him, Johannes tries to increase the passion and consternation Cordelia is beginning to feel. He often takes her to his uncle's house, where a number of droll engaged couples socialize, with the design of getting her to loathe the idea of engagement. He succeeds, and to Johannes' delight, Cordelia's emotions become more and more agitated.
The diary is here interrupted intermittently by Johannes' insertion of notes that he sends to Cordelia, sometimes explaining his intent but other times simply recording them. The notes are brief—not letters, for "the more the erotic is to come out, the shorter they should be"—and try to "develop her mentally, if not erotically." He alternates between detached and intensely personal, between lofty allusions and impassioned pleas. In the letters, he begins to notice that she calls him "mine," but she lacks the courage to say so in real life.
With his subterfuge, Johannes gradually manages to get Cordelia to spurn the idea of marriage. Meanwhile, Johannes reflects extensively about warmth and virginity, doubting that Cordelia would still be interesting to him if they were to be wedded. The only pact to which Johannes adheres to is his "pact with the aesthetic." In the autumn, Johannes silently succeeds in having Cordelia break the engagement herself. Thereafter, he preocuppies himself with ensuring that Cordelia has no opportunity to reflect on what has happened, so that she remains uncertain. Not yet aesthetically pleased with the ultimate irony of his actions, he concludes the journal musing about how "poeticizing himself out of a girl" would perhaps make an interesting epliogue to the Diary.