Others have already synopsized the movie for you, so I will just stick with the fun stuff...
As a longtime fan, I have an old VHS tape with three of Tom Conti's very best performances on it, all recorded off cable back in the late 80's: The Gospel According to Vic; Reuben, Reuben; and Saving Grace. This movie is my favorite of the three. I've probably seen it ten times. I will admit that most of the reason I love the movie hinges on Conti's delicate, relaxed performance. It's damn near perfect.
But you also get some delightful work from the magnificent Giancarlo Giannini. "You're Pope Leo, no? You're Pope Leo, yes." And a hoot of turn by adorable Angelo Evans --- the real life gypsy kid from Robert Duvall's oddball semi-doc, Angelo, My Love --- in his only real acting role. Whatever happened to that kid? He's so cute as the little gangster, Guiliano, whom Conti's character befriends.
There's also a very sweet almost-love-story and some funny stuff by Fernando Rey as Pope Leo's trusted confidante, Stefano. Eddie Olmos provides some menace as the head gangster in Montepetra.
Oh, just see it! You'll love it. I must warn you though that I think they sold the movie way wrong by calling it a comedy. It's a drama with humor. But it's definitely a feel-good flick.
