Toben Betts’ play Invincible has its first half as a comedy, and is delightful.

The second half is full of searing truths, which don’t upset you as much as they should, possibly because they have been heavily foreshadowed in the first half and perhaps because we know these things happen.

Still the change of tone is a shock. Suddenly you are in a different play.

Presented by the Original Theatre Company, this is about class, today, in the twenty-teens.

Professional couple Oliver and Emily move out of London, up North somewhere (it’s not specified) because their income has fallen and it’s cheaper.

They rent because Emily doesn’t believe in owning property. She’s a traditional socialist. She believes it’s her duty to raise standards in the local failing school by sending her child there.

She has set up an arts co-operative and a branch of Amnesty. Her every line is a rant. Every breath is a protest against the government’s “shadow of oppression” hanging over people.”

Those of us arrested on demos in our youth, and for whom Jeremy Corbyn is too middle of the road, see ourselves in her. She is unbearable. A brilliant performance by Emily Bowker.

Her husband, Oliver, played adroitly by Alistair Whatley, the company’s founder and artistic director, tells her: “You are a socialist who doesn’t like people.”

This is a perfectly balanced four-hander but the show is stolen by Elizabeth Boag and Graeme Brookes as the northern, working class, next door neighbours Dawn and Alan.

They are invited in for disastrous drinks. Emily and Oliver don’t drink.

Dawn, who arrives with her beautiful bosom more out of strappy red dress than in it, is a dental receptionist whose hours have been cut: “So I am bored out of my mind for three hours instead of eight.”

Boag’s Dawn has wit and spirit and is never a parody. I loved every movement, she is poetry in motion. Beer-bellied Alan’s mood is determined mostly by the results of the England team.

Emily and Oliver are so alien from his world he just smiles at it. There is no common ground to engage with. Brookes makes him a big, benign man with wonderful pathos in his jolly character. These are two master class creations.

Then Emily goes a step too far. Alan and Dawn can’t ignore her telling them their son is a fool for joining the army.

The first half has been satire. Suddenly we get serious. We sally into the issue of working class soldiers sent to die in wanton wars. Young men whose choice is a factory or the army, sacrificed in conflicts that can never be resolved. Somehow the two halves of the play don’t quite fit together. But the writing is clever, the dialogue is impeccably observed and the performances are invincible.