Before you yawn at the dire predictability of there being yet another white, young, male middle-class comedy pairing on the Fringe, it's worth noting that the splendidly-titled Sisters are unlike most of their competitors in that field. This is mainly due to the bleak, black comedic horror they inflict on their crowd (and themselves every single night) with some sketches and patter which verge on the horrific. All of this is meant to read as a compliment, incidentally.

Christy White-Spunner is the instantly more sinister-looking of the two, with the cold dead-eyed stare of a soon-to-be-caught serial killer while Mark Jones' more obviously pleasant demeanour heads into giggly territory from time to time that is just as unsettling. They kick off with screened footage of them trying to corral support from strangers to their work with the ultimate aim that the online streaming of this performance will earn them hordes of new fans. The slight predictability of that joke's progress throughout the hour is upended entirely when one of their Facebook Live admirers reveals his true nature.

The sheer bleakness of certain sequences and the offhanded in-character way they treat audience participants won't endear them to everyone, but they've given the double act genre a real shot in the arm.

Pleasance Courtyard, until 27 Aug, 7.15pm, £9–£9.50 (£8–£9).