A seemingly Norman Rockwell-like family is at the center of Spencer's (Family Blessings) latest novel, and, as usual, Spencer reveals the hard truths that lie beneath the bright exterior. On the first day of school, high-school principal Tom Gardner thinks his biggest problem is finding the shipment of textbooks for his wife Claire's English class; but the most difficult ordeal of his life is about to begin. Tom's real troubles start when he meets a new student, Kent Arens, who turns out to be smart, well-mannered, a star athlete-and the illegitimate son Tom never knew he had, conceived during a one-night stand 18 years ago, just before Tom married Claire. Tom swings between fear that Claire will find out about Kent and pride in his newfound son, but when the boy, unaware of his lineage, starts courting Tom's 16-year-old daughter, Chelsea, Tom is forced to reveal his secret. Claire, bitter and angry, asks Tom to move out of their home. Robby, their son, resents his new brother and takes out his anger on Kent on the football field. Chelsea, meanwhile, starts running with the wrong crowd. But while Tom and Claire grow farther apart, the three siblings decide to become friends. Together, they reunite Tom and Claire, restoring family harmony. While the course of events is predictable, the characters are warmly drawn and their dilemmas realistic, and Spencer knows how to tug at readers' hearstrings. Chalk up another likely bestseller, the 11th in 11 years for this consistently commercial author. Literary Guild and Doubleday Book Club main selection; film rights to CBS-TV. (Jan.)