This is a pair of affectionate and crisp comedies about sensible British values and social roles (student and teacher, teacher and adjunct, husband and wife, mother and daughter, mother and son).  Bennett is interested in the performances that constitute our public lives: these performances often dictated by gender, class, and, very much part of gender and class, one's role in the family (being a mother, being a son, being a wife, and grieving).  In 'The Greening of Mrs Donaldson', Bennett enjoys the opportunity to describe several medical performances that dominate in medical education.  He ekes a pleasant comedy out of a group of presumably healthy individuals acting our illnesses (the accusation that illness itself is a type of performance is not made here; the ending demonstrates how important it is to tell the difference between the two).  But he really nails that awkward display of terror and blustery confidence in medical students (neither of which is wholly a performance), and, in the figure of Dr Ballantyne, the delicious contempt medical professors have for their students and, at the same time, their earnest desire to be admired by them.  Bennett's subtle insight is that a performance is not merely the artificial imposition of a role over the self, from which a "meaning" can be extracted (the meaning of gender, the meaning of being a grieving widow, the meaning of being a doctor etc.); rather, performances bring meaning to encounters and provide the structure for the self in a particular context; one's integrity comes, in part, from the role one plays.  When the medical students misunderstand the performances of Mrs Donaldson, they misunderstand her.  

Nothing is quite so performative and yet quite so integral to the self as sex.  Sex is often assumed to be disruptive: frequently, that is what makes sex such comic fun.  It causes havoc; most want it, most can't have it, and the mismatch between desire and succor motivates the mayhem.  In these novellas, however, sex is also something that organizes lives: conventional manners control what one says or does not say about sex, creating secrets that are never quite as secret as one might assume or hope; family roles are largely determined by how one avoids the disruptive forces of sex.  The title of the book plays on an assumption that deviance from one's roles leads to smut, but when sex appears in the novellas, it is frequently pleasant and satisfying, even if it lacks certain values that social roles would mandate.