In this 30th entry in one of mystery fiction's longest-running and best-loved series, Spenser--the tough yet sensitive Boston private eye with no first name--takes on an unsolved murder nearly three decades old. The client, an actress, is a friend of Paul Giacomin, Spenser's surrogate son (who first appeared in 1981's Early Autumn). Her mother was slain by leftist radicals at a bank holdup in 1974, and now she wants to know who fired the shot. As Spenser digs into the past, he soon learns that powerful people on both sides of the law want the case left alone--badly enough to kill. These death threats provide a fine excuse for Hawk, Spenser's extremely scary (yet sensitive) bad-guy pal, to tag along in nearly every scene as bodyguard. The interaction of the two friends is one of this series's familiar pleasures, as is the presence of Susan Silverman, Spenser's longtime love interest. Another pleasure is Parker's stripped-down prose, a marvel of craftsmanship as smooth as 18-year-old Scotch. (Plus we get the first meeting between Spenser and Jesse Stone, hero of another Parker series.) Alas, the whole enterprise feels a little tired. The plot never generates much sustained suspense, and the author's adoration for his central characters renders them at times almost cartoonesque. Still, Back Story is excellently prepared comfort food, even if it isn't five-star cuisine. --Nicholas H. Allison