The Swimmer (1968)
Like the movie, Burt Lancaster's title character -- an aging suburbanite who one day decides, on an afternoon lark, to "swim home" pool-to-pool through the back yards of his friends -- starts out lightly charming us, only to plunge into darker waters.
"...D: Frank Perry; with Burt Lancaster, Janet Landgard, Janice Rule, Tony Bickley, Nancy Cushman...."