From the author of several quite varied books for young people (most recently a farcical adventure, The Treasure of Plunderell Manor, 1987), a gentle love story about a couple of teen-agers who meet when the girl comes to stay with her ailing aunt in his New England town. Tom knows Anna is special when he first spies her; their relationship blossoms quietly from the moment they start talking after Mass. But their times alone are rare and often interrupted by normal family and teen-age concerns--his job, the genuine affection of both for Aunt Barbara, his longtime buddy Hank (who's going through a rocky patch after his girlfriend's abortion); still, Tom and Anna's mutual caring and trust grow. When Aunt Barbara suddenly dies, it's Tom and Anna who deal with the hospital and call the relatives. Tom, though, describes his experiences in such copious detail that the story seems too leisurely, if still rich in setting But Clements does pull together much of what threatens to be extraneous in a nifty, brief scene when Tom confirms his love in a verbal confrontation with a young man who had tried to rape Anna a year earlier, and left her blaming herself. In sum, a thoughtful, well-wrought--but slow-moving--exploration of varieties of love.