This is the movie directed by (and kinda starring) Robert Montgomery as Marlowe and shot almost entirely from his POV. Pretty amazing work for the era and size of cameras in 1947. The book is darker and more grisly than the movie, and not set at Christmas, if memory serves. The plot is complicated by the fact the movie never visits the key location from the book, keeping everything in the city and refusing much in the way of exterior shooting.
But, hey, Audrey Totter is terrific. And they actually make Christmas kind of key to the adaptation, so that's fun.