Juliet and Vivian are twin sisters studying at an elite academy of the arts. They both study piano, they both hope to be classical musicians, and they both want to go to Julliard. It is widely thought that Vivian (Madison Iseman) is the more talented twin, and Juliet (Sydney Sweeney) the less successful. It is tough having such fierce competition and such a direct comparison; Vivian isn’t just the better musician, but the better student, the better daughter, the better friend, the better girlfriend. Oh, and she just got in to Julliard. Juliet did not.

It would seem Juliet it is in for a lifetime of second place, but a suicide at her school opens her up to the possibility of a Faustian bargain – is she desperate enough to sell out her own sister, or, just maybe, is getting to sell out her sister the whole point? Nocturne unravels sibling rivalry on a whole new level, and in a way that keeps you guessing as to how much this “deal with the devil” is a literal event, and how much is perhaps just the very idea of it empowering Juliet to come out of her sister’s shadown and challenge her for supremacy. Oh boy.

Director Zu Quirke sidesteps easy chills and obvious gore in favour of something that is more subtle, and far more unsettling. With teenage protagonists you expect something flashy and slashy, blow out parties and surrendered virginities, but this horror is of a more creeping variety, eerie and unknown.

The cast is uniformly solid, but Iseman and Sweeney deliver spell-binding performances that make the tragic relationship between sisters so difficult to crack but so interesting to watch and interpret. Your sympathies may switch teams several times before the last act, which is predictable, yes, but dizzying and vital. The horror bits are actually Quirke’s most conventional beats; her strength is in story-telling. The academic setting is both cutthroat and ripe for predation and exploitation. The interesting is figuring out who, or what, is behind it all.

Nocturne is one of four “Welcome to the Blumhouse” horror offered in a bundle on Amazon Prime. Stay tuned for more reviews, and be sure to let us know if you’ve taken the plunge.