Classic, British period, Hitchcock railway mystery from 1938 on BBC iplayer, here https://www.bbc.co.uk/iplayer/episode/b0078kyh/the-lady-vanishes
and here is a previous post about this film https://bagdcontext.myblog.arts.ac.uk/2014/12/23/the-lady-vanishes-alfred-hitchcock-1938/