The clue even comes up in some of his titles: The Pitchfork Disney, Dark Vanilla Jungle, Tender Napalm. Sweet'n'sour is more than just Ridley's favourite Chinese takeaway. The competing flavours battle at every level of his work (director Eve Nicol memorably defined this as 'tickles and terror). Cosmo Disney, the cockroach eating urchin in Pitchfork and Cougar Glass (from The Fastest Clock in the Universe) are seductive and repulsive in equal measure - the latter, with his taste for young boys, shares a sweet tooth with Disney's protagonists The Stray Twins. Never mind the amount of confectionary devoured by the characters: Ridley laces his treats with rat poison.
He brings chiaroscuro across into playwriting, but his facility for the telling phrase and the extended monologue gives the impression of an almost conservative writer. He subtly undercuts the audience's understanding of events, questioning the reliability of the characters' commentaries.
It is this mixture of dark and light, the chiaroscuro, that defines Ridley's scripts and makes the violence all the more chilling. Like a good classical author, however, Ridley doesn't revel in the on-stage representation of cruelty. The threat hangs heavy, and occasionally breaks out into a ruck, but the atrocities tend to happen off-stage or, in the case of Pitchfork, in the protagonists' dreams.
Even in his most narrative driven works (Dark Vanilla tells a story from beginning to end, albeit through a very unreliable narrator prone to black-outs), Ridley carves a reality both familiar and alien. Familiar in so far as the props and places are recognisable (chocolate, consumed to excess; stuffed birds; paedophile rings) but alien in that the characters are isolated in their own worlds. Cougar pretends he is young, so as to better seduce teenagers, The Stray Twins keep the doors locked. Even when he does get physical (Ghost from a Perfect Place has a girl-gang getting medieval on an old gangster's ass), Ridley frames it within a universe that veers violently from mood to mood, never dropping narrative for a surreal rush but always challenging the surface impression and hinting at bleaker depths.
Ridley's background - he is also a visual artist and a filmmaker - may have encouraged his adaptation of Dark Vanilla, the young woman could be either sympathetic victim or deceitful abuser (she's both) and whether she is villain or heroine is never established: Pitchfork features detailed descriptions of dreams that appear to contain elements of the play's previous scenes.
There's a lovely sense of Brecht's alienation effect at work - the characters are always distanced from the audience, ambiguous - and Ridley juggles the fundamental division in theatre (between what is actually happening on stage, and what that is supposed to represent) until it is impossible to decipher whether the scripted action is set in reality or is a more symbolic psycho-drama. Tough stuff indeed, and a reminder that the cool, searching intelligence can upset the format without losing a dramatic punch.