help to ID music clip of a famous piece of music taken from a tv series

hi, my memory is very bad and i have heard a famous piece of classical music on a agatha Christie TV drama. i have researched everywhere to identify it and had no luck. the frustrating thing is that i know i have it in my large collection of classical music, I've been playing loads of my stuff to try and find it but with no luck. i have attached a very poor quality clip of the music, recorded using my pc from the drama via the TV speaker, so hence the bad quality. i would be delighted i [...]