TWO mysteries, one by old pro Robert Parker and the other by newcomer Alex Juniper, while touching on the usual fare of greed and retribution, focus primarily on love for a young person.In Parker's latest mystery, "Pastime," his famous bull-necked yet witty private investigator, Spenser, continues what he started in "Early Autumn" (1981): helping a young man grow up. The book, six weeks on the New York Times bestseller list, manages to combine a delicately nuanced psychological study of family relationships with a hard-boiled mystery. In the earlier novel, Spenser was hired by Patty Giacomin, a manipulative woman locked in a child-custody battle with her ex-husband to get her son back. Instead, he sizes up both seedy parents and takes the boy off to straighten him up through carpentry and sage advice. In "Pastime," Paul, now a graceful 25, is thinking of marriage and wants to settle some unfinished business with his mother. The problem is, she has disappeared. So has her mobster boyfriend, with a substantial amount of the mob's money. So Spenser agrees to help him find her. "Helps" is the key word here. In this more leisurely mystery, Spenser lets Paul be the main drive behind the search. For his part, Spenser gets to do what he does best. He knows how the mob operates and how to talk to them. But his role here is more as a sounding board for Paul, who is trying to come to terms with his mother's abandonment of him. Along the way, Spenser reveals details about his own boyhood that can help Paul in his growth into manhood and help the reader understand how the private eye got to be so self-reliant. Reading both "Pastime" and "Early Autumn," one gets not only a sense of the shared context, but also sees the evolution of Parker's writing. Spenser, in the terse style of Raymond Chandler, packs plenty into a short sentence. And he's also known for his repartee with his right-hand man, Hawk, and Susan, his unflappable "significant other." But the wit's more mature now, less forced. BUT back to the mystery. Patty's boyfriend has gotten in trouble with the mob, which picks up the clues of the couple's location in western Massachusetts at the same time Paul and Spenser do. A shootout at a house in the woods ends with the mob chasing a wounded Spenser though the woods. That's the high point of the action. Spenser's common-sense love for Paul is counterbalanced by that of the mob boss for his own son. The father goes to great lengths to prepare his incompetent, cowardly son for the mob career he's clearly unsuited for, as well as trying to protect him from his own undoing. The ending is satisfying, if not particularly dramatic. This is not a book for great fireworks. But it's another good chapter in the continuing life of Spenser. And with Parker, one always gets a great look at the streets of metropolitan Boston - from the tony suburb of Lexington to the "dim halos of mist" around lights on Boston Common. Alex Juniper's book, "A Very Proper Death," rivals Parker's on that score, but picks other Boston locales: the boarded-up, crack-infested neighborhood of Jamaica Plain and a Back Bay mansion, replete with Royal Albert china and Bokhara rugs. Like Parker's novel, the story also explores familial love. From the first page, the novel is taut with tension. Real-estate agent Marni Verstak gets a 2 a.m. call from a man threatening her son's life - a son no one is supposed to know exists. She's kept his whereabouts secret since his birth five years ago, when she was in the process of getting an annulment of her marriage to the boy's father, who is gay. The child has been secretly living in Vermont with Marni's best friend and her husband. That's plot one: Who's the voice on the phone and why does he want to harm her son? Plot two has to do with a formerly dilapidated house in a bad neighborhood that Marni turned into an oasis of loveliness. She has a vision of creating low-income housing by hiring homeless men to renovate, and bringing in the city to provide low-cost mortgages and financing. But someone doesn't want this deal to go through: One of the homeless workers, a friend from Marni's youth, gets killed. How these two apparently unrelated plots finally merge is a tribute to Juniper's imagination and mostly skillfu l writing. There are elements that make you cringe, however: names like Giraint Finnbar, Anderson Thorpe III, and Ainsley Wilson. And a breathless romance-novel love scene is jarring. But don't let that stop you. It's refreshing to read a mystery that is low on body counts, lunacy, and viciousness.