I just re-watched the most recent "Murder on the Orient Express" where our venerable detectibve is played again by David Suchet. There is much more French in this new series, and in the case of this particular episode, more religion. The whole episode is very dark, and nothing like the Peter Ustinov version from the 1970s. In one scene, we see Poirot, on his knees with his rosary in his hand, and he prays something like "je te rends grace que tu m'as fait catholique" (I think thee that thou hast made me Catholic). This is juxtaposed with the victim-to-be praying almost like an evangelical, though being Italian-American, that is unlikely. Again later, we see Poirot thinking hard with his rosary in hand.
Also, there is a dialogue between Poirot and a Scandanavian protestant where said protestant scolds Catholics for believing that all sin is forgivable. This is, of course, no more a part of Protestant doctrine than it is of Catholic doctrine. And of course, it is much more a part of the plot than of any theology.
I hope I don't spoil this for anyone. The plot of this episode is nearly as well known many Bible stories.
The more recent episode, aired last night, contains no religious references at all, and I think anyone who sees the two will agree that the darkness of the Orient Express episode does not continue into the second episode. The second includes such favorite actors as Zoe Wanamaker and Peter Bowles.