In fact Isaac has a son by a previous marriage, although that fell apart when his wife Jill (Meryl Streep) left him for another woman. He is currently mortified with the news that she is writing a book about their life together, raking through the emotional debris. Yale introduces Isaac to Mary, although he finds her abrasive and pretentious, in contrast to the loving and mature beyond her years Tracy. However, Isaac and Mary meet again, quite by chance, and Isaac realises that her behaviour is just a facade. She is really just as lonely and confused as he is, hence they become friends (not lovers though, because Isaac would never do that to Yale). The web of relationships becomes ever more tangled as Mary fights with Yale (she doesn't want to waste her life on a married man and he doesn't want to hurt Emily), after which they split up. Yale knows the difficulty Isaac has reconciling his affair with Tracy and suggests that he and Mary team up instead. Isaac jumps at the chance.
Almost brutally, Isaac brushes Tracy off, using her youth to suggest that she doesn't know what's good for her while he does. Coming from someone who's already been through two marriages this is difficult to take, but Tracy has little choice (of course, she should go to London to study but that doesn't make it any easier). An excellent scene ensues when Emily meets Mary for the first time, as Isaac's lover, with an undercurrent of emotion running between the menage-a-trois. In the midst of this chaos, Isaac quits his job as a comedy writer for TV and settles down to write his novel, partially spurred on by Jill's revealing book (which is a huge success). However, Yale and Mary are still deeply in love and start seeing each other again. Nothing has changed with respect to Emily though. The shock spurs Isaac into re-examining just what's important to him and who he really cares about, with an uplifting result.
Manhattan is a tremendously amusing movie, that much is obvious, and Woody Allen displays all of his gift for exquisite dialogue. However, the story works at a deeper level by finding resonance with our greatest fears and highest hopes; these are our emotions on the screen and the depiction is spot-on. Throughout the movie we develop an intense rapport with the characters, aided by the excellent acting and their individual qualities. The photography (in black & white) is stunning, stretching from delightful compositions of Manhattan landmarks to intimate, emotional moments. The love of Allen for New York seeps through every frame, a characteristic which exists in many of his films but never as strongly as in Manhattan. The icing on the cake is the energising score, taken from compositions by George Gershwin. In summary, Manhattan is a life-affirming and gorgeous experience without flaw.