Reader beware: I go into detail about the content of the story after the cut.
I read this story in Penguin's anthology of eleven of Munro's short stories about love, entitled "The Progress of Love."
Lichen, which takes place in a small town by Lake Huron, is about a divorced couple, David and Stella. They have been divorced for eight years at the start of the story, although they were married for much longer than that; they're probably in their mid- to late-forties. David, with his girlfriend Catherine, is visiting Stella at her cottage home, as he does every year for his father-in-law's birthday. Together, they visit the senior's home where David gives the 90-year old the same gift he always does: a bottle of Scotch whiskey.