I stepped out of the National Theatre in a state of numb horror. I was without words. Usually I come out of a theatre with all my thoughts and opinions bubbling up in my mouth, but this time I was left completely inarticulate.

I wanted to know how actors put themselves through Medea every night for weeks, not to mention the days spent in rehearsal working scenes over and over again. This doesn’t just go for the leads, either. The whole cast, including the incredible chorus, were in the story the entire time.

The set for Medea was astounding and very important to the plot, so I’ll start there. The stage in the Olivier Theatre, one of several located within the National Theatre, is enormous. Both wide and deep and accommodating 1,150 patrons, this is no intimate black box stage. Upon entering the theatre, the audience walks into a peaceful domestic scene where two boys watch TV, huddled in sleeping bags on the floor. The house looks like something you might find in a bad part of town, but it is warmly lit and coloured. Above it stretches a balcony and a glass-encased room, both of which prove essential to both the chorus and the all-important wedding that takes place at the same time as the main action below.

The first person to speak is the children’s nurse (Michaela Coel) who introduces the characters and events leading up to the beginning of the play. When the time comes for her to introduce Medea (Helen McCrory), the nurse disturbs the sense of warmth and safety by pulling aside the partition to reveal deep woods that seem to go on for at least twice the width of the apartment. Trees grow in the dark, and among them Medea crawls, screaming, feeding the fire that burns in a metal drum.

From this point on, the audience bears witness to the terrible story of Medea’s revenge on her husband Jason (Danny Sapani), who has run off with a young, pretty, and wealthy girl. McCrory plays a gritty and down-to-earth Medea, ripping through the text (and into other actors) as if they were dead leaves in her path. She enters the play trembling with hot rage that cools and moulds itself into definitive action.

The chorus is a fascinating aspect of Greek tragedy that can be difficult to make speak to modern audiences. A dozen or so women all standing behind one idea and motivation is not something that happens often in contemporary plays. Here, director Carrie Cracknell turns the chorus into bridesmaids at Jason’s wedding. They side with Medea’s cause but caution her against what will happen if she decides to execute her ultimate revenge on Jason: killing her own children. They also act as personification of Medea’s psyche: they begin in neat, 1950s-style dresses, but by the end of the play the dresses are torn and the hems, as well as the women’s feet and legs, are covered in mud.

Medea almost listens to her advisors and brings her revenge only to the point of killing Jason’s new bride. Haunting music plays, and at the last minute she stabs her pajama-clad sons offstage while the audience sits and listens to them scream. Medea wraps their bodies in two sleeping bags that she clutches and will not let go, denying Jason even the privilege of burying his children.

The most terrifying image for me, and the one that left me speechless for several hours after the show, occurred in the last few moments of the play. After stabbing her children and explaining her motivations to a grief-stricken Jason, Medea hoists one body over each shoulder and carries them into the forest, barely able to support their weight, trembling now from physical weakness and grief.

The night was cool when I stepped out of the National Theatre. I crossed the Jubilee Bridge amid crowds of tourists and buskers, but all I could see were flashes of Medea, her back to me, hauling her two dead children into the forest. Medea gets what she wants, I thought. But she pays a very high price for it.