The first act takes place outside a spa overlooking a fjord. Sculptor Arnold Rubek and his wife Maia have just enjoyed breakfast and are reading newspapers and drinking champagne. They marvel at how quiet the spa is. Their conversation is lighthearted, but Arnold hints at a general unhappiness with his life. Maia also hints at disappointment. Arnold had promised to take her to a mountaintop to see the whole world as it is, but they have never done so.
The hotel manager passes by with some guests and inquires if the Rubeks need anything. During their encounter, a mysterious woman dressed in white passes by, followed closely by a nun in black. Arnold is drawn to her for some reason. The manager does not know much about her, and he tries to excuse himself before Squire Ulfheim can spot him. Unable to do so, Ulfheim corners him and requests breakfast for his hunting dogs. Spotting the Rubeks, he introduces himself and mocks their plans to take a cruise, insisting that the water is too contaminated by other people. He is stopping at the spa on his way to a mountain hunt for bears, and he insists that the couple should join him, as the mountains are unpolluted by people.
Maia takes Ulfheim up on his offer to watch his dogs eat breakfast, leaving Arnold alone with the mysterious woman. He quickly realizes that she is Irena, his former model. Irena constantly refers to herself as being 'dead'. During their conversation, she explains that posing for Arnold was akin to a kind of 'self murder', where he captured her soul and put it into his masterpiece, a sculpture called 'Resurrection'. He confesses that he has never been the same since working with Irena. Though 'Resurrection' brought him great fame and an abundance of other work, he feels a similar kind of death as Irena feels.
Irena mysteriously alludes to killing all of her lovers since posing for Arnold. She claims to always possess a knife, and also admits to murdering every child she has had, sometimes while they are still in the womb. When Irena asks where Arnold is going after his stay at the spa, she dismisses the idea of the cruise and asks him to meet her up in the high mountains. Maia returns with Ulfheim, asking Arnold if they can abandon the cruise and join Ulfheim on his mountain hunt. Arnold tells her that she is free to do so and says that he is thinking of going that way himself.
The second act takes place outside a health resort in the mountains. Maia finds Arnold beside a brook. She has spent the morning with Ulfheim. The couple return to their discussion of Arnold's unhappiness, and he confesses that he has grown tired of Maia. He wants to live with Irena because she had the key to the lock which holds his artistic inspiration. Their relationship was never sexual, because Arnold felt it would have ruined 'Resurrection'. Maia is hurt but insists that Arnold should do as he pleases. She even suggests that perhaps the three of them could live together if she cannot find a new place to live.
Irena enters, and Maia urges Arnold to speak with her. The pair cast flower petals into the brook and reminisce sentimentally about their long-ago collaboration. At one point, Arnold refers to their 'episode', and Irena draws her knife, preparing to stab him in the back. When he turns around, she hides the knife. Arnold asks Irena to come live with him and work with him again, explaining that she can unlock his artistic vision once more. She insists that there is no way to resurrect a partnership like theirs, but they agree to pretend they can. Maia returns with Ulfheim, on their way to a hunt. She is happy and explains that she feels like she is finally awake. She sings a little song to herself, "I am free...No longer in prison, I'll be! I'm as free as a bird, I am free!"
The final act takes place on the rocky mountainside, with narrow paths and a shabby hunting hut. Maia and Ulfheim enter already in an argument over his sexual advances. Maia demands to be taken down to the resort. Ulfheim points out that the path is too difficult for her and she will surely die on her own. Arnold and Irena come up the path from the resort. Ulfheim is surprised that they have made it on their own, since the path is so difficult. He warns them that a storm is coming. Since he can only guide one person at a time, he agrees to take Maia down the path, and urges Irena and Arnold to take shelter in the hut until he can return with help.
Irena is horrified at being rescued. She is convinced that the nun will commit her to an asylum. She draws the knife again to kill herself. Arnold insists that she should not. Irena confesses that she almost killed him earlier, but she stopped because she realized he was already dead. She explains that the love that belongs to their earthly life is dead in both of them. However, Arnold points out that they are both still free, insisting that "we two dead things live life for once to the full". Irena agrees but urges that they must do it above the clouds of the gathering storm. They agree to climb the mountain so that they can be married by the sunlight. As they happily ascend out of view, Maia's song is heard in the distance. Suddenly, an avalanche roars down the mountain. Arnold and Irene can be seen carried to their deaths. The nun has followed Irena up the mountain and witnesses the horror with a scream. After a moment of silence, she says "Pax vobiscum!" (Peace be with you), as Maia's song still lingers in the air.
Output: Why do Arnold and Irena agree to climb the mountain?