The play begins with a haunting prologue in which the Narrator reveals the tragic ending before the story even begins. We see Mrs. Johnstone described as a woman with "a stone in place of her heart" — a reflection of society’s judgment. The Narrator asks:
"Did you ever hear the story of the Johnstone twins…? How one was kept and one given away?"
This immediately establishes fate and inevitability as key themes.

Mrs. Johnstone, a struggling single mother in 1960s Liverpool, is left to raise her many children alone after her husband walks out. When she discovers she’s pregnant with twins, she panics, knowing she cannot afford to raise two more children. Her wealthy employer, Mrs. Lyons, unable to conceive, offers to take one of the babies and raise him as her own. Though hesitant, Mrs. Johnstone agrees, believing it’s the only way to give the child a better life.

They make a pact — but Mrs. Lyons is quick to manipulate her:
"You won’t tell anyone about this, Mrs. Johnstone, because if you do, you will kill them."
This fabricated superstition becomes a driving force of fear and secrecy.

The twins grow up separately: Mickey stays with Mrs. Johnstone in poverty, while Eddie is raised by the affluent Lyons family. But fate brings them together by chance when they meet in the street as children and instantly become best friends.
They declare:
"We’re blood brothers, aren’t we?"
Neither boy knows they are, in fact, real brothers — a dramatic irony that haunts the entire play.

Mrs. Johnstone is terrified of them spending time together, but Mrs. Lyons becomes even more disturbed by their growing bond. She spirals into paranoia and fear, eventually deciding to move house in an attempt to separate them permanently.

Years later, Mickey and Eddie reconnect as teenagers, still unaware of their true relationship. Eddie is now a well-educated and polite young man, while Mickey has grown up tough and street-smart. They are reunited with Linda, who is now Mickey’s girlfriend but admired by both boys.

As the pressures of adult life mount, the cracks begin to show. Mickey loses his job in the economic downturn:
 “They’ve started layin’ people off in the other factory y’ know.”
He becomes depressed and desperate. Meanwhile, Eddie thrives at university and eventually becomes a councillor. The difference in their social classes becomes clearer — and more painful.

When Mickey gets involved in a robbery with his older brother Sammy, he ends up in prison. Traumatized, he returns home a different man, now dependent on anti-depressants.
 "Leave me alone, will y’? I can’t cope with this”
His relationship with Linda suffers, and she secretly turns to Eddie for help — a move that ignites Mickey’s jealousy and paranoia.

The Narrator returns throughout Act 2, reinforcing the sense of doom and inevitability with recurring lines like:
"The devil’s got your number."

In the final scene, Mickey bursts into the town hall with a gun, confronting Eddie in a jealous rage. The truth is finally revealed: they are twins, separated at birth.
Mrs Johnstone says "Mickey. Don’t shoot Eddie. He’s your brother. You had a twin brother. I couldn’t afford to keep both of you. His mother couldn’t have kids. I agreed to give one of you away!”
But the revelation comes too late. In the chaos, Mickey accidentally shoots Eddie, and the police shoot Mickey moments later. The play ends with the haunting image of both brothers lying dead on the stage.

The final lines echo the prologue, with the Narrator asking once more:
"And do we blame superstition for what came to pass? Or could it be what we, the English, have come to know as class?"