The Saint In London - 1939 - 6/10

Templar is approached by a government friend and asked to investigate one Mr Lang.
Soon turns out Lang has his hands in all sorts of nasty pies.
Early on, Simon (suave George Sanders) hires a valet whose last place of residence was San Quentin.
Also a female admirer, determined to help.
Unlike a lot of private eye flicks, Templar here relies on his support team (who are not mere comic relief).
The police likewise are pretty sharp, as are the villains, especially Mr Lang.