The delightful Miss Marple...

She has many incarnations on films and TV but the best, the greatest, was Joan Hickson's BBC version. Filmed 'straight' with no gimics and, again, a wonderful theme tune, this series was very faithful to the original books which were excellent. A charming old lady ran rings around the police, noticed everything, knew everyone's foibles and always came to the right conclusion.
However, there was one other version, staring Margaret Rutherford, in a series of films in the fifties and sixties. These were a bit camper and blew holes in the original stories but were fun anyway.