The Invisible Adolescent : FADE <i> by Robert Cormier (Delacorte: $15.95; 310 pp.) </i> : THE MERMAID SUMMER <i> by Mollie Hunter (Harper & Row: $12.95; 119 pp.) </i>

First off, I loved “Fade.” Couldn’t put it down. There’s no question that Robert Cormier is an exquisite, tight writer, as proven in his celebrated “The Chocolate War” (1974) and now, in this fantasy that Delacorte Press is marketing for age 12 and up. It is, however, twice as long as the average young adult book and there are passages that will make some parents jump from their seats.

“Fade” is not for kids.

During the summer of 1938 in Frenchtown, Canada, 13-year-old Paul discovers that he has the power to become invisible. What fun, he at first thinks: He can avenge the town bully, play tricks on people or, better yet, observe private lives. Unfortunately, Paul’s spying unveils “dark and nasty secrets it was better not to know about(.)” He is so horrified by the unnatural sexual acts he witnesses (described clearly), his “Catcher-in-the-Rye” innocence is lost. After he stabs a villain to death, he vows never again to turn invisible. Thus ends the novel’s first half.

Now flash to 1988. Susan has just finished reading “Fade,” a final manuscript of the now-deceased Paul, the world-famous writer who was also her cousin. Susan and Paul’s literary agent are trying to decide if “Fade” is truth or fiction, and if it is truth, how utterly incredible. Cormier’s novel now moves back and forth between Susan’s narration, Paul’s, and Paul’s nephew, 13-year-old Ozzie who has inherited the fade.

The destruction and bloody deeds unleashed by Ozzie are unsettling, partly because the reader is vicariously involved, another testimony to Cormier’s skill. But most of all, it’s frightening to think what an unhappy adolescent--or any of us for that matter--would do if no one could see us. Cormier seems to be saying that we have dual natures and depending on who’s watching us, two faces.

My disappointment is not with the author, but with a publisher who misleads its audience. “Young Adult” is very much different than “Mature, Almost Adult.”

“The Mermaid Summer” (ages 8-12) should be read aloud in front of a warm stone hearth by someone with a Scottish burr. Set in a fishing village during the 1800s, the story tells of “a mermaid who ruled the cold, wild sea that washes around northern lands.” She is a cruel mistress who lures boats onto rocks and blackmails the townsfolk with her power.

Eric Anderson so fears for his life that he leaves the village to work aboard an oceangoing ship, far away from the creature’s spell. After three years at sea, his grandchildren, Anna and Jon, ages 12 and 13, decide the only way they’ll ever see him again is if they trick the mermaid. If they can tame her, then it will be safe for Granda Eric to return. By ingenuity, bravery and a little help from the town medicine woman, the two kids succeed in doing what no one had ever done before.

Mollie Hunter unwinds her tale as spontaneously as a village storyteller. Suspense builds perfectly. As one of Scotland’s foremost writers for young people, she shares the rhythm and language of her countryfolk so well.