Like a fog-shrouded hill, "The Merry Gentleman" might slip by you unnoticed. Don't let it. This small gem of a movie is the first directed by Michael Keaton, who stars along with the exceptionally talented young Scottish actress Kelly Macdonald. We see in the film what Keaton has refined as an actor -- that ability to know exactly how to play each emotional note for maximum effect. Which means he never underplays or overplays this quiet love story that develops between a young battered wife trying to lose her past and herself in a new city and a hit man trying to reclaim a remnant of his soul. The dialogue is exquisitely spare, a gift from screenwriter Ron Lazzeretti, and the Christmastime Boston that cinematographer Chris Seager has conjured up is yet another present under the tree.