Valentine and Chloe, wearing Regency clothing, sit at the table, while Gus tries on things for the party. Chloe reads from the paper about Bernard’s published work, “Even in Arcadia – Sex, Literature, and Death at Sidley Park.” She adds that even though people say the future is programmed like a computer, sex always messes it up. Valentine replies that this is the “attraction that Newton left out” and it all goes back to the apple in the garden (78).
Hannah comes in, sneering at Bernard’s article. Annoyed, Chloe takes Gus with her to help him find an outfit.
Hannah and Valentine flirt a little, and he tells her that her “classical reserve is only a mannerism; and neurotic” (79).
They start to work quietly for a bit, and she asks about the grouse, and tells him not to give up. He asks if she thinks it is trivial, and she laughs that it all is, but “it’s wanting to know that makes us matter” (80). He shows her “The Coverly Set” that he made in the computer and how it made “islands of order” in “an ocean of ashes” (80). This is the result of plugging in Thomasina’s equations millions of time, which she was not able to do.
When he comments that Thomasina would have been famous, Hannah tells him that no, she would not have, because she died in a fire the night before her seventeenth birthday. Valentine remembers this story. They turn back to their research.
Lord Augustus bursts into the room where Thomasina studies with Septimus; she is now sixteen. He smirks and plays, and Septimus asks if he shall join them. He says imperiously that he is at Eton. Thomasina shows Septimus her rabbit equation in which it eats its own progeny.
Hannah closes the book and turns to a garden book. Valentine speaks of how the process of heat going cold is a one-way street. It is happening everywhere and will happen to everyone someday. He explains that even if Thomasina or her tutor understood this, they were not fully ready to yet – “You can't open a door until there’s a house” (83). Genius is only for lunatics and poets.
Thomasina asks Septimus if she will marry Lord Byron. Absorbed in her lesson book, he says no, and that Byron is not aware of her existence. Augustus continues to act peevish, and eventually leaves.
Thomasina says he is mad because she told him Septimus kissed her. Septimus asks when he did that, and she says last night in the hermitage when he promised her he would teach her to waltz and then they sealed it with a kiss. She insists she simply must learn how to waltz for London.
Septimus shows her an essay he is reading in which the author claims, “the atoms do not go according to Newton” (85). The piano plays next door as Thomasina reads. When it goes silent she does not notice but Septimus does. Lady Croom comes in and seems startled to see them. Septimus rises but she motions him to sit.
The piano and the steam engine are heard. Chloe enters. Lady Croom asks for Noakes.
Valentine tells Chloe to be quiet. Lady Croom apologizes for the disturbance and complains of the monotony of the steam engine. Thomasina distractedly asks what she talking about, and Lady Croom closes the door. Hannah takes notes.
Lady Croom asks what Thomasina is learning, and Thomasina replies, drawing and geometry. She then talks about how she can almost forgive her brother’s marriage because of the amazing dahlias sent. It is good, then, that the monkey bit the husband and not the wife.
Thomasina is triumphant after reading the essay, and speaks of heat and how “determinism leaves the road at every corner” (88). Her mother says she must be married soon, and Thomasina says it will be Lord Byron. Her mother asks if that is so, and asks where Septimus saw him last. Septimus says Fuseli was sketching him.
Noakes enters and Lady Croom complains about the steam engine and her destroyed garden. She asks why he built a hermitage without a hermit there; he is baffled and says maybe he could advertise.
Thomasina tells Noakes that his steam engine will never get out of it what he wants. She gives him a diagram and, confused, he thanks her. Noakes and Lady Croom leave, and Thomasina sketches Septimus with Plautus the tortoise. He thanks her for the drawing.
Thomasina leaves and Augustus comes in, bashfully saying he wants to ask Septimus some things about sex that he cannot ask his friend. They plan to go for a walk later.
Bernard enters, furious and ashamed, claiming he is now “fucked by a dahlia!” (93). He begs Hannah to tell him if it is all over, and has her read the passage in the garden book about the death of Chater and the marriage of Mrs. Chater and Brice. The poet Chater is thus the same Chater who described a dwarf dahlia in Martinique and then died of a monkey bite. Bernard is incredulous and realizes how much he had promoted his book in the media. He wonders how long it will take before it gets out, and Hannah says she will write a short, dry, and polite letter. Though terrible, it is better than one of his friends doing it.
Chloe is upset that Bernard will be leaving, and tries to get him into costume for the party; her family is always photographed by the hermitage. Bernard groans and pulls something over his face.
Light changes, paper lanterns glow. Piano music plays.
Thomasina, dressed in a nightgown, enters with a candle. Septimus is already there, reading. He is startled to see her. She kisses him and says he is paid, and must teach her to waltz. She sees him reading her essay and sits down with him.
The party is happening now. Valentine and Hannah come in the room and he starts looking for a paper. He finds it – the diagram. His words and Hannah’s mix with Thomasina’s and Septimus's. They are all doomed, heat can’t run backwards. The universe will grow cold. All anyone can do is waltz.
Bernard enters, tearing off his costume clothes and saying he must go now.
Septimus and Thomasina waltz and kiss again.
Chloe comes in, furious and distraught. Her mother caught them in the cottage. She begs Bernard to let her go with him, but he says no. He then apologizes profusely to everyone. He tells Chloe it was wonderful, and, as he leaves, tells Hannah he hopes she finds her hermit. She says she has an idea who it is but cannot prove it.
Thomasina is delighted that she is waltzing.
Hannah sits down with wine amidst the papers.
Thomasina prepares for bed and waltzes once more with Septimus.
Gus enters, dressed perfectly in period clothes. He hands Hannah the drawing of Septimus and Plautus. He bows at her as an invitation to dance. She demurs at first but then accepts. They dance awkwardly.
Septimus and Thomasina dance fluently.
Various threads of the story now come together, occasionally concluding, occasionally remaining open. There is comedy and tragedy, love and death. The chaos of the Romantic garden in Sidley park manifests itself in the chaos theory of Thomasina (nascent, of course), and Valentine. In this final scene, characters from both eras occupy the same space, touch the same objects, and occasionally have their words overlap and mingle. Stoppard has conflated time, although he still finds ways to demonstrate the divide between the eras, especially in the linear development of the science behind Thomasina’s musings, which Valentine says had to wait patiently for time to pass before being able to be fully realized.
Bernard’s theory about Byron killing Chater is definitively debunked, and he comes to realize how embarrassed he will be after the world realizes that he was wrong. His self-interested quest for knowledge and smug assumption that he can truly understand the past are thoroughly rebuked by Stoppard. The type of scholarly pursuit we should be engaged in is one in which the journey is valued for what it is, in which the love of knowledge is more powerful than the desire for fame or money. Hannah articulates this when she admits to Valentine that all they are doing – the grouse, the hermit – is trivial, but it is “wanting to know that makes us matter. Otherwise we’re going out the way we came in” (80). She is, as critic David Guaspari writes, “playing for higher stakes” than Bernard, and “it is she who sees deeply enough to put Thomasina at the center of both stories.”
Thomasina’s story is the most tragic, for as the play comes to an end, she has both found a way to explain her theories and prepares to ascend the stairs to her death. The steam engine is one of her biggest clues, as it becomes apparent the engine cannot be a perpetual motion machine - some of the energy (the heat) is always lost.
It is Chloe, the least academic person in the group, who finds a way, albeit a pithy one, to explain the same principle Thomasina described. She says sex is what complicates the order of the Newtonian universe – it is that same “heat” that negates determinism. The heat is there in the universe until it runs out, and it is there in the dance of the characters until they stop. As Guaspari writes, “even here is death, but also the possibility of love and a harmony of knowing and knowing. For so long as Septimus and Thomasina delight in this final lesson, death will be kept at bay, and time and loss will be, for an Arcadian moment, overcome.”
Thomasina and Septimus have their own type of heat, giving the mostly comedic play a tinge of tragedy. He becomes the hermit in the hermitage, spending the rest of his days trying to bring her equations to fruition, which is insane since it cannot be done without computers. He knows the tragedy implicit within the equations – that the universe is growing cold – but he is “desperate to overturn this pessimistic conviction through restoring pattern and the promise of life in an ocean of ashes,” as Paul Edwards writes.
That final scene, with its collapse of time, is telling. As Johann Hari writes, “the division that obsessed the 18th century – between romantics and classicists – exists in all of us. Hannah prides herself on her classical reserve, but, by the final scene, it is faltering. She finally agrees to dance with Gus… He is a symbol of all the things that lie beyond her rational explanations –and she embraces him.” Humans need to be both “classical” and “romantic” or our lives will not have meaning.