The meaning of the title "Fallen Angel" is not apparent until about halfway through the film. I will discuss it below, after the "SPOILERS" warning. Sinise plays a very successful attorney in L.A., leaving Maine after his graduation because he and dad were not close, and he wanted "to become more" than caretaker of vacation cottages in Maine. He comes back upon news that his dad is ill. A key element of the story is being reunited with a girl he had not seen in 30 years.
SPOILERS follow, read further at your own risk. As a boy, he had been in a car that accidentally killed a mom and child in the winter, the shocked dad went off into the woods, was written off as dead, the 9-year-old boy was in the back seat comforting the 4-year-old daughter. When he returned as an adult, the grown girl coincidentally was arranging to spend Christmas in the cottage, they reunited but she had no memory of the early childhood. Her dad was not dead, he was a street person, in the winter they would go into parking garages and partially lay on warm hoods of cars, and looked like 'fallen angels', thus the name of the movie. Eventually the daughter and dad were reunited, and the two grown kids fall in love. Just a sweet, typical Hallmark movie where everything turns out for the better.