Isaac Davis (Woody Allen) is feeling more than a little guilty about his romance with Tracy (Mariel Hemingway) in Manhattan. She's 17, has an opportunity to study in London, and has her whole life in front of her. He's 42, twice divorced, neurotic, and driven to question why life is worth living. At the same time, Yale (Michael Murphy), Isaac's best friend, also is feeling guilty about his affair with Mary (Diane Keaton). She's divorced, insecure, and needy. He's married, loves her, but loves his wife, too. With George Gershwin's music to guide them all through the hustle and bustle and lingering beauty of New York City, Isaac, Tracy, Yale, and Mary dance the eternal "relationship dance." They examine and reexamine their liaisons, break up, form new allegiances, and fall in love all over again. And beneath the excitement, hurt, joy, and disappointment they enjoy and suffer, they're struggling with the weightiest elements of the human condition: self-respect, integrity, loyalty, fear, and love.