Yuppie With a Yippie Girlfriend : MYSTIC LAKES <i> by Damian Musello (Donald I. Fine: $17.95; 290 pp.) </i>

Damian Musello’s engrossing “Mystic Lakes” is that rare first novel which is about something, featuring not only a plot, but also a smorgasbord of complex social and political issues. On its surface this is a story of ‘60s political activists struggling to survive in the yuppified ‘80s. At its core, however, it is about justice and history and rebellion and, most of all, about consequences.

Narrator Derek Anderson has made his accommodation, rebuilt the life which blew apart in a botched political explosion, served his five years in prison and come to believe that “maybe we gave too much thought to things.” Derek makes his living now as a Boston private detective, ferreting out employee theft and serving as local bodyguard for visiting entertainers.

Marion Wilson, Derek’s one-time lover and political cohort, has made no such compromises. Underground 15 years since the bank explosion which injured Derek and killed another friend, Marion has remained politically active. She’s a rather formidable figure: “Marion was the complete political person. All that she was came from give-and-take, interaction, a constant mechanical, radar-like reflection of her personality onto others--the dense vibration of will and thought echoing out and coming back, altered, from which she sensed strength, weakness, the validity of thought or emotion.”

Though still firmly committed to her revolutionary ideals and actions, Marion has plenty of humanizing contradictions. She’s sufficiently purist not to shop in supermarkets that are “consolidating the distribution of food in this country,” for instance, but perfectly willing to buy weapons from the Aryan Brotherhood to ship to rebellious South African blacks.

At the same time Derek is being reluctantly pulled into a bitter internecine struggle between local Teamster factions, Marion drops back into his carefully-reordered life, trailing a phalanx of rumors, criminal charges, ambivalent confederates and an ambitious junior FBI agent who “was three years old when Martin Luther King said, ‘I have a dream.’ ” Derek finds himself drawn to her again, even though his tenuous foothold in society--not to mention his pistol permit--could be easily brought down again by this woman who “had no home, no stable center for her life, except perhaps a collection of books, an abstract ideology, a calling as isolated and harsh as a monk’s.”

“We talked in large nouns then,” Derek remembers, with the hindsight of 15 years. “Our enthusiastic, educated minds were filled with grandiose concepts begun with capital letters and that we were taught as children in school: Liberty, Independence, The Fraternity of Man. The young think in grand terms, single words, broad concepts. As we grow old we become more concerned with nuances, the adjectives and adverbs of life, the structure of sentences--commas, semicolons, periods.”

“Mystic Lakes” blends those nuances into a compelling reminiscence, a tale that moves effortlessly between past and present, told by an author wise enough to realize that there are neither simple solutions nor “correct” answers.