Greg, 15, put that hair in the toothbrush of sister Megin, age twelve. "Sibling rivalry," says Dad, a stubborn Pollyanna type. More like "sibling homicide," mutters their weary Mom, who has lately turned to spells of self-hypnosis in order to remove herself from the battlefront. And Spinelli, using Greg and Megin as alternating narrators, offers a breezy yet fierce, often slapsticky evocation of brother/ sister hostilities here--while giving the two kids believable other concerns too. Greg calls Megin "Megamouth"; he's appalled by her filthy room, sure that she'll bring on an infestation of cockroaches. ("They're having the World's Fair for Bacteria in there.") But Greg's primary interest in life is beautiful Jennifer Wade, for whom he's redone his appearance (bodybuilding, "Sassooned" hair, etc.); and he blithely exploits the crush of not-so-pretty Sara to make contact with her elusive friend Jennifer, repenting later. Meanwhile, Megin calls Greg "El Grosso," incorrigibly plants a cockroach in his room, and provokes him into food-fights. Her affections belong instead to kiddie-brother Todd; to ice-hockey idol Wayne Gretzky; to a friendly Dunkin' Donuts waitress (who gives her freebies); to fellow tomboy Emilie, 89, a chance acquaintance whom Megin visits regularly in a nearby nursing home; and to classmates like ordinary Sue Ellen and extraordinary Zoe--a newcomer from California who fills a bra and wears green toenail polish. Will Greg and Megin eventually reach a genuine truce? Of course. But only after the warfare gets out of hand (violence on the ice)--and after Emilie's unexpected death brings Megin to the breaking-point. . . and Greg to the brotherly rescue. (As it happens, the quest for Megin's beloved, sunken hockey-stick winds up with sister saving brother.) As in Space Station Seventh Grade (1982), then, Spinelli keeps things very light most of the way through, shading into more serious feelings--with considerable finesse--only at the end. So the upshot, if never really distinguished, is bright, personable, and reasonably lifelike--with nice average kids, unusually low-key/amusing parents, and a sure balance between farce and sentiment.