After two consecutive murders, the police hires young criminologist and lecturer Dimitris Lainis to help.

Dimitris discovers a suicide and a fatal accident prior to the murders also have the number 220 and Pythagoras's quotes.

A police officer informs Dimitris that all the victims participated in a trial regarding the death of Kleio Rapti.

After attending a lecture by French mathematician Marcel de Chaffe, Dimitris learns about "eteros ego", translating to "the other me".

Dimitris discovers the murderer is Kleio's best friend Danae, who owns a similar amulet with the number 220.