Famous singer Emilia Marty appears to be greatly interested in the case, without revealing her motives.

She gradually reveals intimate knowledge of the 19th-century nobleman and his household, along with personal experiences from the French Revolution.

Emilia turns out to be Elina Makropulos, a woman from Crete who was accidentally granted a centuries-long life through a decision of Rudolf II, Holy Roman Emperor.

Described by Čapek as a "comedy", Věc Makropulos received its first performance on 21 November 1922 in the Vinohrady Theatre in Prague.

The play was produced in translation at the Arts Theatre in London, under the name The Macropulos Secret, on 8 July 1930.

The producer was A. R. Whatmore and the cast included André van Gyseghem as Vitek, Lesley Wareing as Krista and Donald Wolfit as Jaroslav Prus.

Čapek also attempted to qualify criticism of his philosophical point of view, with respect to the idea of extended human life span, as pessimistic.

Albert Gregor comes in to ask about the case, which Kolenatý has taken to the Supreme Court, where he is waiting for a final resolution.

Emilia states that Ferdinand Gregor was the out-of-wedlock son of Baron Prus and an opera singer, Ellian MacGregor.

Kolenatý leaves, and Albert tells Emilia that if he does not win the estate, he will be penniless and shoot himself.

They found the will where Emilia said it would be, and Jaroslav congratulates Albert on his victory – if he can prove that Ferdinand Gregor was the Baron's out-of-wedlock son.

The empty stage of the opera house A stagehand and a cleaning woman discuss Emilia's performance.

Kristina tells Janek that they cannot continue their relationship, because she needs to concentrate on her singing to become a great artist like Emilia.

Emilia enters, but spurns them all, including Janek, who instantly falls under her spell, and Albert, who brings her expensive flowers.

There is a further similar discussion about Jean-Paul Marat and the French Revolution, where again Emilia expresses strong opinions that appear to derive from her direct experience of the people and events, even though they occurred 120 years earlier.

At first, Emilia treats him with disdain, but then he states that she seems to resemble Eugenia Montez, a Romani woman with whom he had an affair in Andalusia half a century before.

Emilia softens her attitude, and then engages Hauk-Šendorf in conversation in Spanish, reminiscent of his past times.

Jaroslav proceeds to ask Emilia what she knows about Ellian MacGregor, whom he describes in disparaging terms, after reading her love letters that detail explicit sexual behaviour.

Jaroslav grieves at his lack of showing affection to Janek, but Emilia is indifferent and asks if she has to tear her hair out every time someone dies.

Emilia explains that Emperor Rudolf II wanted his court alchemist to prepare a potion that would grant him 300 years of youth.

Kolenatý remains disbelieving of Emilia's story, and accuses her of forging the signature of Ellian MacGregor and stealing the locket of Eugenia Montez.

Kolenatý starts to realise that Emilia may have been telling the truth during the whole of this "trial", as does Jaroslav, who admits that Gregor has the right to the inheritance.

Kolenatý, Gregor, Jaroslav and Vitek then engage in a discussion about the implications of the "Věc Makropulos", this formula for 300 years of youth.

Jaroslav argues that the intellectual elite of men (no women at all) should be granted this elixir, with weaker people allowed to die normally.

Emilia returns to the room, and explains that she wanted to retrieve the "Věc Makropulos" to gain another 300 years of life.

However, she tells everyone that her extended life has led to exhausted apathy and a sense of cynical futility about people.

Emilia finally offers it to Kristina, saying that this formula will allow her too to become a great singer, and to live for 300 years.

The "Věc Makropulos" slowly catches fire, to the momentary dismay of the men, such as when Hauk-Šendorf asks for just a small piece of the parchment.

Czech novelist and playwright Ivan Klíma summarised Čapek's thematic intent of the play as follows: Klíma also expressed his opinions on aspects of the final scene as follows: Věc Makropulos features in the philosophy essay "The Makropulos Case: Reflections on the Tedium of Immortality" by Bernard Williams.

In his essay, Williams utilizes the case of Elina Makropulos to argue that an immortal life should not be desirable.