Lazarus Plot, The (Hardy Boys Casefiles #4) by Franklin W. Dixon

Murder is only skin deep.

Camped out in the Main woods, the Hardy boys get a real jolt when they glimpse Joe's old girlfriend, Iola Morton. Can it really be the same girl who was blown to bits before their very eyes by a terrorist bomb? Frantically searching for her, Frank and Joe are trapped in the lair of the most diabolical team of scientists ever assembled. Twisting technology to their own ends, the criminals create perfect replicas of the brothers. Now the survival of a top-secret government intelligence organization is at stake. Frank and Joe must discover the bizarre truth about Iola and face their doubles alone --- before the scientists unleash one final, deadly experiment.