KIRKUS -- In this seventh installment, the sleuthsfrom Griswold's Grammar School unravel yet another case involving a mysteriousportal and a time-bending troublemaker. Once again, the six young Britishgumshoes find themselves in the midst of something both puzzling and strange. Aspuberty looms, the group-three girls and three boys-has become divided alonggender lines. The girls begin to watch an unusual student who is always-andsomewhat anachronistically-rambling on about communists, while the boys startinvestigating a malevolent trio of classmates. With the discovery of a wormholein their science lab and the changing of recent events, the group must convergeand figure out a way to stop the time-traveling wrongdoers from rewritinghistory. As Allison's series has progressed, the characters have aged with it,bringing increasing complexity to each case but maintaining its whimsy and nevertaking itself too seriously. Like its predecessors, this volume relates acomplete case and works well as a stand-alone, though it has enough quietin-jokes to reward devoted followers. Allison's attention to detail in hischaracters is playful, with an especially keen eye to his protagonists' stylishsartorial choices. However, those seeking diversity may be happier elsewhere;his mainstays are nearly all white, save for one who is black. A delightfullyquirky series whose eccentric charms haven't faltered. (Graphicmystery/fantasy. 10-14)