Kate is a teenager staring out into the audience and smiling and muttering. A young busker stands in a corner playing his guitar. The set is a single park bench. In the gloom of this Underbelly space my heart sank Ive seen a lot of plays in Edinburgh down the years where youre presented with this kind of spare scenario as you enter. It doesnt usually bode well for riveting entertainment. I neednt have worried. Every so often (though maybe not often enough), the Festival unearths a little gem and this piece sparkles as brightly as any Ive seen.Enter Richard. Hes wretched, as hes just been told the terrible news by his doctor that he will be unable to father a child. He gets talking to Kate and from this unlikely alliance we get to explore some incredibly deep themes, most fundamentally of all, what it means to be a man.And its all done with consummate professional skill. Tom Spencers short, new script is perfectly paced under his own direction and both actors, Robin McGloughlin and Holly Beasley-Garrigan are superb, though the latter doesnt quite look young enough to play a teenager. Richard tells Kate that having weighed up the options (surgery that probably wont work, adoption) he and his wife Amy have decided to go down the path of using a sperm donor. What follows is a series of imaginings about the future, beginning with the moment Richard is handed his baby by a nurse. He looks at it, and realises that it doesnt and will never look like him. Its heartbreaking. Were then taken through other imagined scenarios, culminating in a furious row with his teenage daughter who screams at him You cant tell me what to do, youre not even my real dad.Im making this all sound a little bleak; it really isnt. Its full of great wit and gags. Kate speculates on what it would be like to find out your biological father was someone who grunted over a cup, and makes a funny, though insensitive remark about seedless grapes. Theres nothing po-faced about the treatment of the subject matter, and the real strength of the production is its warmth and humanity. The staging is simple but brilliant, a red anorak becoming actual characters in front of our eyes. The guitar music, written and performed by James Hill (the busker) always enhances but never intrudes or tries to cheat our emotions.I wont be spoiling it to say theres a pretty happy resolution. If I have a slight criticism it is that this ending is a little too pat, a bit too easy after all weve heard. Kate tells Richard about here own situation with her mother, who clearly resented her existence. Its this information that allows Richard to move forward and embrace the future.The day I saw this there were about twelve in the audience. Ive sat in some packed auditoria for the last three weeks watching some terrible acting, students murdering the classics, directors intellectually wanking off, performers not having a clue what the play they are undertaking is about. All of them should see this play that they might see how simply, if you have the talent, you can make people laugh and cry. And think. Everyone involved here should be very proud of their new baby.