I think that the story starts on page twelve, when Elaine McGill (wife of prominent dermatologist Paul McGill) is boinking horn-dog medical student Mike Traynor in a tourist cabin.
("Don't worry," she says. "My husband plays golf every Wednesday afternoon.")
She desperately wants a baby for her husband, and is willing to go to any lengths to get one. Any lengths. She can't go to the clinic to get artificially inseminated, though, because then her husband would find out and would know it wasn't really his. She picked Mike because, as a student, she can tell him that if he breathes a word he'll get flunked, and because he looks like her DH.
He does her. Then, he notices that she didn't have an orgasm, so he does her again, and this time she does (leaving her feeling Very Guilty). She's also convinced that this time it took and she's now all pregnant and everything.
Mike heads out trying to make it back to the hospital before his shift in the ED starts, and at that moment the news comes on the radio that Lorrie's been plugged by her hubby. "Holy Crom!" Mike says, or words to that effect, "If he'd come home early a week ago that woulda been me!"
Thus ... Mike as main character. And, thus a good starting place.