Radio Play is a programme that plays in Colin's head.
It's a particularly interesting programme about the history of the mouth organ.
When Colin meets Beth - the new receptionist at the doctor's surgery, she seems to be able to hear Colin's radio programme too.
The problem is Beth doesn't hear quite the same things as he does.
She's quite certain the programme is about the balalaika.
Is this, as Doctor Proctor suspects, an extraordinary phenomenon in modern psychology or is there something more universal at work?