Simon Stockdale spells it out for his son Jack: "Your grandfather is proposing to leave your grandmother to whom he has been married for forty years and marry a woman with whom he has been having an affair for seven years".
What can this mean to a boy in the throes of his first love affair? Or to Simon's wife Carrie, who always thought her wronged mother-in-law was one of the most self-pitying women she'd ever met anyway? Filial debts are about to be called in and Carrie doesn't want her husband Simon to pay them. Yet Simon feels a bond of obligation towards his mother which makes him vulnerable - and which no one else can fathom.
And what of the mistress - a barrister who has fallen in love with a judge twice her age? What if, as Simon's gay brother Alan decides, she's the real thing - she's a proper person? . . .