The ninth month, like some people, refuses to admit what it is; a time sequence spanning thirty days with a Roman name revealing a curious human quality, it suffers from an identity crisis. The days are usually too cold for tennis in Fairfield County, but today, perhaps as an unexpected welcome to Jane, the weather had the soft dreamy balm of a spring day. She heard the thwack and twang of a ball hit well as she approached the tennis court from the rear driveway. She got out of her aqua Mini Cooper and decided to watch for a while before surprising her mother, who was crouched low in the forecourt waiting to receive service. Nancy, in any case, wouldn't interrupt the game, so it was just as well for Jane to restrain herself. Nancy Teller Siddley played with the measured grace and cobralike anticipation of someone who had been taught very young by a pro with style. Her opponent was not Jane's father. Although less assured in his strokes, he had the clumsy power and determination of a slum kid who had spent hot summers with a tennis permit on the city's concrete courts.