FICTION : WHERE ALL THE LADDERS START by Ron Loewinsohn (Atlantic Monthly: $17.95; 223 pp.).

It is perhaps unfair to judge one book by another, but given that Ron Loewinsohn’s second novel, “Where All the Ladders Start,” is a quasi-sequel to his first, “Magnetic Field(s)” (Knopf, 1983), one can’t help but look back comparatively--and with a bit of longing.

For unlike “Magnetic Field(s),” which was violent and disturbing drama, “Where All the Ladders Start” is a relatively uneventful story of a not entirely successful composer/conductor, David Lyman, who, in the throes of mid-life crisis and assisted by a young composer/musician lover, struggles to piece together a psyche alarmingly fragmented by long-term marriage with a preoccupied nuclear freeze groupie and a son possessed by punk rock. The weakness is not in the time-worn tale, but in the central figure, who is simply not interesting in Loewinsohn’s treatment. After reading “Magnetic Field(s),” from which Lyman emerged, one may also question the choice of protagonists here--any number of other characters, left beautifully suspended, could have provided stronger substantive material. Loewinsohn’s second novel does share a propensity for music with his first, but while “Magnetic Field(s)” is music--with rich, tonal subjects masterfully intertwined into a fuguelike structure--”Where All the Ladders Start” is simply about music, the objectification of which falls surprisingly flat.