THE INVISIBLE WORM by Jennifer Johnston. (Carroll & Graf: $19.95; 192 pp.) Novels can be so painfully, excruciatingly interior . Really, we're only readers, not therapists. These authors should take their characters with all their problems to some nice couch and pay the big bucks. Use hand puppets. We have our own problems. Of course it's possible that the more you feel like running in the other direction, the closer they've come to a real life nerve. Or the thing is just badly written and trite. This novel is neither. The main character, a recluse who shares the home she inherited on the brooding Irish coast with her skin-deep husband, is spending a lifetime dredging up a childhood memory that we see looming all over her life from the very beginning of this short book. A new friend, a man, helps her to clear away the brush surrounding an old summerhouse on the property. He doesn't really ask any questions, he just spends time with her. It becomes clear that something terrible, unspeakable happened in the summerhouse. But when she finally reels this memory in, this horrific rape of a child by her father, then what? A revelation, and life loosens its grip a little.