The detective fiction I return to most is not Agatha Christie — who is technically brilliant and emotionally unsatisfying — but the earlier work of Arthur Conan Doyle and the later work of P.D. James. Both writers understood that the detective novel's real subject is knowledge: what can be known, what cannot, and what it costs to find out.

Holmes knows things that shouldn't be knowable and the stories are partly about the pleasure of watching extraordinary reasoning. James's Dalgliesh knows things that are knowable through care and patience and the knowledge doesn't bring satisfaction, because the people who are dead remain dead.

These are two different philosophies about what knowledge is for, expressed through the same genre. The contrast is one reason I read both.