The scene has changed to the present day, apparent from the clothing of the characters on stage. The setting is still Sidley Park, but there have been changes in the surrounding landscape with time. The modern day characters, Hannah, Chloe, and Bernard, sit in the same room as Thomasina and Septimus. Hannah, a writer in her thirties, sits and leafs through the pages of Mr. Noakes's sketchbook. Chloe, daughter of the home, and Bernard, a visitor, enter from another doorway. The two enter a room that has been cleared out because the family is hosting a dance for the district. At the dance there is generally much drunkenness, and the room, en route to the nearest toilet, has been cleared out to avoid thievery and vomit. Bernard has come to talk with Hannah about the estate, and Chloe goes to look for her. Gus, the mute oddity of the estate, looks through the doorway from which Chloe exited but quickly goes away. Valentine, the son of the estate, next enters the room and exits by the door at the opposite end of the room. He is apparently looking for an available toilet.
Valentine returns to the room and finally takes notice of Bernard. Bernard introduces himself to the distracted Valentine who vaguely remembers talking to Bernard on the phone the day before. Valentine finds his tortoise, Lightning, under the bed. Valentine leaves to take the tortoise on his run. Hannah finally enters. Chloe has told Hannah that Bernard's last name is Peacock rather than Nightingale and addresses him as "Mr. Peacock." While Hannah scrapes the mud off her boots from the garden, Bernard raves about Hannah's book, Caro. Hannah is annoyed at Bernard's gloating and threatens to leave, but Bernard then mentions Ezra Chater. Bernard brings The Couch of Eros from his bag and reads the inscription; "To my friend, Septimus Hodge, who stood up and gave his best on behalf of the Author-Ezra Chater, at Sidley Park, Derbyshire, April 10th 1809".
Bernard is looking for information on Ezra Chater. Hannah tells Bernard that she hasn't found anything on Chater in the records of Sidley Park. Hannah is looking for information on the Sidley Hermit, whose death she attributes to the breakdown of the romantic imagination. Mr. Noakes, the gardener of Sidley Park, actually built a hermitage, specifically as part of the landscape of the estate. The hermit was added as a piece of landscape, just as a pottery gnome. When the hermit died, the hermitage was found filled with papers with mysterious proofs written about the end of the world. Hannah thinks that this hermit's work and life is the perfect symbol of the Romantic Period, a century of rigorous intellectualism that turned on itself.
Chloe walks through the room and addresses Bernard by his real name, Mr. Nightingale. Hannah now knows Bernard's true identity, the academic who criticized her work in the Observer. Hannah is furious, and Bernard has difficulty keeping her in the room. Bernard tells Hannah he wants to collaborate with her on a project. Apparently, Bernard's copy of Ezra Chater's The Couch of Eros belonged to Lord Byron. Inside the book there are three documents that have led Bernard to believe Lord Byron killed Chater in a duel. Bernard believes that Lord Byron slept with Chater's wife, Chater challenged Byron to a duel, and Byron ended up killing Chater in the duel. Because Lord Byron left the United States in 1809, soon after Chater published his last known work, Bernard assumes he was fleeing the murder. Hannah distrusts Bernard. She assures Bernard that she has found no evidence of Lord Byron at the estate, and she believes he has never been there. Through a bit more conversation it is revealed that Septimus Hodge and Lord Byron went to Trinity together. Bernard believes that this fact is proof of Byron's presence at the estate. Chloe enters as Bernard leaves triumphantly. Chloe tells Hannah that her brother, Gus, is in love with Hannah. Gus, of course, is the mute and, apparently, brilliant brother who wanders in and out of the scenes. Gus enters and gives an apple to Hannah.
Arcadia, by intertwining two stories of the past and present of the same family, begs a particular question: what is the meaning of self and how does one know it? The stories are strictly separate plots, settings and worlds; however, there persists the same question of identity for all characters.
The sameness between characters is revealed through the pairing and intertwining of people and objects on stage. While the stories progress separately, each story has a distinct presence in the other until the final conclusion of the play, where the stories fully overlap and the characters seemingly talk to one another. The nineteenth century tale (that of Thomasina and Septimus) is reminiscent of a classic romantic comedy of errors—involving the requisite cuckolds, unrequited love, desperate lovers, affairs, word plays and so on. Thomasina's social world has little consequence and is limited to the affairs of Sidley Park. The modern tale (that of Hannah and Bernard) reveals a broken comedy of errors—the dysfunctional and broken aristocratic family whose only source of excitement is a Regency ball for the community. The modern aristocratic society is one that must look to the past for prestige and entertainment.
Nonetheless, both societies and peoples are seeking themselves and the knowledge of the future and present. The play doubles time and characters to reveal constant truths between past and present. Valentine, the son of the absent modern Crooms and math scholar lacking significant discovery is paired with Septimus Hodge, former scholar and hermit of Sidley Park who works equally hard with similarly little result. The two share identical turtles, Plautus and Lightning, that have the same identity and value to their owners. Like the identical turtle props or taxidermy, the actor of Gus and Augustus Coverly is the same. The young boy of both generations has changed little, besides the fact that Gus is mute, while Augustus is tirelessly loud.
Thomasina and Chloe are another pair. The "action of bodies in heat" argued for by Thomasina manifests in Chloe's complete concern with the heat and seduction of Bernard. Like Thomasina's discovery of the second law of thermodynamics, Chloe adds her own idea to the mix: sex is the ultimate argument against determinism. Chloe believes that the randomness of sexual attraction keeps the world from a deterministic end. Like her counterpart, Thomasina, Chloe asks if she is the "first person to think of this." Valentine, like Septimus, replies to her enthusiasm with a probable "yes." The ultimate proof to the random nature of bodies in heat exists in Thomasina's generation with the character of Mrs. Chater—a woman obsessed with making heat with anyone at anytime. Chloe seems to know the proof of her idea by her own actions and attraction to the foppish scholar, Bernard. The second law of thermodynamics, while possibly not fully understood by either girl, is simultaneously an answer and a dilemma to the question of self for the girls;one cannot predict the random actions of people or themselves. The death of Thomasina by fire is certainly symbolic of this truth.
Strangely enough, the modern tale, besides the presence of Chloe, is much lacking in heat, which may explain the lack of introspection by either Bernard or Hannah. Hannah, like Thomasina, distinguishes and separates love from academic progress. Hannah continually denies and refuses love or affection from Valentine or Bernard. Bernard, while failing to understand academic or real truth, has a good understanding of self. Bernard suggests to Hannah that, if she had understood herself better, she would have not written her first book about Caroline Lamb. Chloe, who seems to understand herself better than either Hannah or Bernard, turns psychologist to Hannah, saying, "You've been deeply wounded in the past, haven't you?"
The law of the amorous Mrs. Chater rules the ability for one to find self- knowledge within Arcadia. In the past and in the present, if one cannot understand the randomness of love and canal knowledge, he or she will certainly fail to understand him or herself.