I will tell you in a general way about the story, since it is not my intention to tell you all the details, so if you are a fan of this kind of plots, you need to see it and you can create your own opinion of it, The story starts with Elizabeth Sparkle (Demi Moore) doing a tv show where she is an aerobics trainer and together with her group she is in charge of showing the public an exercise routine to keep in shape; When the owner of the channel fires her he makes it clear that he needs a younger woman to be the new image of the program, she leaves the building devastated and has an accident in her car, before being discharged from the clinic her nurse gives her a card with a video about a program called “The Substance” and she keeps it in her pocket indicating that they can help her, When she sees herself in the mirror she looks ugly and old, although she wears make-up and dresses in a sexy way her body is no longer in conditions to show herself with the image she had before when she was admired by everyone.

Estas inseguridades se intensifican más cuando ve en el periódico que están llamando a un casting a chicas de 18 a 30 años para tomar su lugar en el programa, recordando la tarjeta que le había dado el enfermero y cuando llama le dicen que con este experimento ella tendrá otro yo, que podría reemplazarla por una semana y tendría la oportunidad de hacer la vida que ella quisiera, pero deberían seguir unas reglas para sobrevivir las dos, ella acepta y le entregan un kit con la sustancia que debe inyectarse sin saber que estaría iniciando su peor pesadilla.

These insecurities are intensified when she sees in the newspaper that they are calling for a casting for girls from 18 to 30 years old to take her place in the program, remembering the card that the nurse had given her and when she calls they tell her that with this experiment she will have another me, that she could replace her for a week and she would have the opportunity to make the life she wanted, but they should follow some rules to survive both, she accepts and they give her a kit with the substance that she must inject without knowing that she would be starting her worst nightmare.

A este punto de la historia se nos presenta a la audiencia el surgimiento de este otro yo, una mujer joven que sale de su cuerpo específicamente de su columna quedando ella tirada en el suelo de su baño por una semana, alimentada por un suero, y esta nueva persona debía inyectarse por una semana el fluido de su medula espinal para poder estabilizarse, para luego hacer el cambio y ser ella quien pase una semana descansando con el suero. Toda esta locura que le acabo de decir es presentada en una escena sumamente perturbadora que ocurre en un baño donde ambas están desnudas, y para serles sincera estuve a punto de dejar de ver la película hasta aquí.

At this point in the story the audience is introduced to the emergence of this other self, a young woman who leaves her body, specifically her spine, and she is left lying on the floor of her bathroom for a week, fed by a serum, and this new person must inject herself for a week with fluid from her spinal cord in order to stabilize herself, and then make the change and be the one who spends a week resting with the serum. All this madness that I just told you is presented in a very disturbing scene that takes place in a bathroom where both are naked, and to be honest I was about to stop watching the movie until here.

La trama continua cuando Sue (Margaret Qualley) se dirige a la televisora para hacer el casting y gana el puesto de Elizabeth, todos le alaban su belleza y juventud semana a semana y la hacen sentir superior a todos, ella se lo cree y empieza a subir su ego a tal punto que ya no quiere cambiar con su matrix, a su vez quiere quedarse con su vida más tiempo, extrayéndole más y más fluido de su medula espinal que hace que Elizabeth empiece a deformarse, acá se pone aún más fuerte las escenas; ya que Elizabeth prácticamente se transforma en una anciana toda deforme, que aunque trata de terminar con este experimento ya los cambios en su cuerpo son irreversibles.

The plot continues when Sue (Margaret Qualley) goes to the television station to do the casting and wins the position of Elizabeth, everyone praises her beauty and youth week after week and makes her feel superior to everyone, she believes it and begins to raise her ego to such an extent that she no longer wants to change with her matrix, in turn she wants to stay with her life longer, extracting more and more fluid from her spinal cord that makes Elizabeth begins to deform, here the scenes get even stronger; since she practically transforms into a deformed old woman, and although she tries to end this experiment, the changes in her body are irreversible.