Outside the Yard, there are warning signs: "Big Guns contains scenes of imaginary violence." It's a good joke. Do we really need trigger warnings for violence that won't actually happen? Are we such snowflakes that we need shielding from our own imaginations? Spare us the thought of bloodshed. Deliver us from the mere idea of evil.

The signs have a serious side too, though - deadly so. Nina Segal's swirling script, almost a staged poem, draws a direct line from small acts of virtual violence to actual, all-out atrocities. Violence needn't be real to have real consequences.

Just as Sarah Kane tied domestic abuse to the extremities of war in Blasted, so Big Guns stitches our online cruelties into the real world. They're not just on the same spectrum, Segal insists. They're part of the same system. Rosie Elnile's stage is a literal slippery slope.

It's not a huge revelation. Not any more. Fake news and stolen emails have swung elections. Innocents have been beheaded for YouTube. Trolls have taken to Twitter, and teenagers have taken their own lives. Social media has been a springboard to revolution.

Segal starts microscopically, though. She writes butterfly effects into being, so that tiny transgressions ripple off into the wider world. Her debut In In the Night Time (Before the Sun Rises) extrapolated from the cries of a sleepless child to the roar of riots outside, to screaming sirens.

Form works hard. Segal almost writes in word clouds: voices ping-ponging back and forth, lapping at one another's sentences. Their words entwine. Images entangle. Narratives blur. Everything comes to feel connected. A man with a gun, silent and threatening, sits behind a collection of cyberbullies. He seems to hold the whole play hostage. Is he real or symbolic?

Someone, somewhere, flicks through a discarded diary - an innocuous invasion of privacy, but one that nonetheless entails some seeds of unwarranted judgement. It might seem victimless - the author, Em, will never know - but it's still a betrayal, one human to another. A troll picks apart two bloggers, Ike and Kay, scouring every scrap of content for weaknesses to expose and scabs to pick. A vlogger, Leila, blocks out vulgar comments. Her videos - make-up tips and shopping hauls - attract lascivious viewers.

Watching's key. Debra Baker and Jessye Romeo start in 3D specs, square-eyed and somehow inhuman. They guzzle popcorn and gorge on hot dogs. There are two of them - ‘me' and ‘you,' us and them. The moment two people see each other, Segal implies, they size one another up. There's a choice: collaborate or compete, engage or objectify. She never loses sight of that. It's as if the man with the gun calls the shots.

Segal's form aims for a symphony of language. Too often it slips into word soup. Expressionism masks unevenness, but scripts like this must make each word count.

Big Guns needs more nuance than Dan Hutton's staging provides. Katharine Williams basks the whole thing in the hot pink glow of old Soho sex shops. Kieran Lucas underscores it with film music – threatening strings and menacing bass riffs that work like the de-dums of Jaws. It's edge of the seat stuff. Or, at least, it should be.

If the aim is to up the intensity, to run a power surge through the whole play, the actual effect is to flatten it out. There's meaning in that - a mark of the way we acclimatise to the drip, drip, drip of day-to-day violence until it no longer even registers – but it does rather douse cold water on Segal's script. Her writing snowballs. Here, it peters out. It's as if Hutton has highlighted every line. All the inherent violence is signposted right from the start - earlier, even. It winds up with nowhere to go.

Big Guns runs at the Yard Theatre until 9 April.