In Howard Colyer's Homework (at the London Theatre until 1 December) the cruelty of dementia is laid bare, its devastation of a brain, and a relationship, revealed by telephone conversations that reminds us of the condition's casual cruelty.
Vincent (Jonathan Benda) is alone in his flat scraping a living as a writer and (probably) living off his redundancy from a previous job in a bank. His mother (Jean Apps) is in her 80s, living in a home and has dementia. She calls her son and they talk - but such is dementia's grip on the old lady that the temporal is lost and memories, incidents and people pour forth unanchored by any sense of time. Vincent is asked repeatedly about how his now dead brother is getting on (suffering the pangs of that loss over and over again); he is chided for his drinking as if still a naughty teenager; and he is (perhaps most cruelly) reminded of his status as least favourite, youngest son - an afterthought and an accident - dementia also destroying his mother's sense of empathy.
Though some of the absurd juxtapositions of dementia raise a laugh or two and there's a wonderfully warm episode of lucidity when Vincent's mother recites a speech from the Merchant of Venice, word perfect, 70-odd years on from its learning for a school play. But such moments are exceptions, as the play concentrates on how the dementia takes two ordinary decent people and tortures them.
There's a lovely chemistry between the two actors which, allied to the simplicity of the set-up, makes their situation all the more tragic. With medical science promising us that today's babies will live to 100 years of age, degenerative conditions like dementia will affect more and more of us - and it's not going to be pretty.