"You hit your sixties and seventies and there is the danger of becoming less thought-rich,” Ian McEwan said in a 2018 interview. Published in his mid-seventies, his 496-page new novel abundantly displays that this is an impoverishment he hasn’t yet experienced. Thought — “the brief privilege of consciousness”, as the hero of his 2005 novel Saturday calls it — has long been McEwan’s signature subject.