Richard Pratt, a famous middle-aged wine connoisseur, is having dinner with the Schofields for the third time. Twice before, he has won a case of wine from Mike Schofield by correctly identifying the claret served with dinner. This time, Pratt wishes to increase the stakes - he offers his London house and his place in the country against the hand in marriage of the Schofields' teenage daughter, Louise. And Schofield (who is sure he has found a wine no one could identify) persuades Louise to agree to the bet. After all, this wine is unguessable...