The study of twins and the genetics of aggression totally consumes research scientist Jeannie Ferrami. An accomplished and headstrong researcher, Jeannie has developed a sophisticated software program to identify identical twins reared apart. But Jeannie's breakthrough project is threatened by the appearance of a sudden impossibility--identical twins born weeks apart to different mothers at separate locations. When Jeannie's research assistant, Lisa, is raped, Steve Logan, a young law student who is one of Jeannie's research subjects, is identified in a police lineup as Lisa's attacker. Logan's genetic tests reveal no violent behavior patterns. Then Jeannie stumbles upon the beginnings of a stunning revelation. Logan is unaware of the existence of a criminal twin brother in jail. Jeannie is convinced of Steve's innocence, yet her judgment may be clouded by her growing emotional attachment to him. By now Jeannie's problems are mounting. Berrington Jones, Jeannie's arrogant and intimidating boss, is a world-renowned authority on biotechnical engineering. He and his partners are involved in devious but lucrative negotiations to sell Genetco, their biogenetic research company. Jeannie's research poses a major threat to their impending millions. Jones arranges to have Jeannie fired.