he falls under a moving train and is killed.

It looks like an accident but a photographer friend of Giordani happens to take some photographs of the accident and little Lori recognizes the fair-haired man from the car in one of them. Arno is suspicious and talks to Giordani about it. Meanwhile, the photographer has discovered in the picture an arm pushing the fair-haired man onto the railroad track. Arno and Giordani rush to the photographer's studio where they find him strangled, his face slashed with a razor.

Giordani and Arno, who reveals himself to be a former journalist, decide to pursue their own private investigation of these horrible crimes.

Giordani starts by speaking to Terzi, his beautiful and snobbish daughter, Anna (CATHERINE SPAAK), and several others at the Institute. Professor Casoni explains to Giordani that at the Institute studies are going on into a chemical product which may correct hereditary defects, and research is being made on the XYY factor-a deformation of the genetic pattern which could predispose an individual to murder.

Bianca, at Arno's suggestion, looks for some clues among her dead fiance's papers, and finds a little note. But before she can give it to Arno, she, too, is viciously murdered.

Giordani, with the help of a friend, (a weird hippie burglar), makes a nocturnal visit to Terzi's home. There he finds among the professor's papers a document which reveals that Anna is not his real daughter. Also, he finds out that there has been an abnormal relationship between them.

In the next few days, Giordani turns his investigation to Professor Brain, a homosexual leading a double life. But when he goes to talk with Braun, he finds him killed by a knife in his own home. He is stumped momentarily; but the idea that the clue that Bianca had found might be in the little locket that she was wearing when she was buried, occurs to Arno.

At the cemetery the two steal into the family crypt where they find the note in the locket. But they are forced to hand it to the murderer who, without making himself seen, has followed them and tells them that he has kidnapped Lori and is going to kill her. But Arno and Giordani succeed in finding Lori and her kidnapper's frail, After a violent hand-to-hand fight with Giordani, the murderer manages to escape . .