Trikymia mias kardias (1969)

Unbeknownst to him, Alekos Anastasiadis, the young atomic scientist of the Greek Institute of Nuclear Technology "Demokritos", has fallen prey to an invisible secret agent who watches his every move. Intent on stealing Alekos' important research, the dangerous operative will stop at nothing to succeed, including putting in jeopardy the scientist's already unstable relationship with his wife, Nora. Under those circumstances, everyone is a suspect, and, above all, an enemy; however, is Lena--the seductively beautiful stranger--too, part of a devious grand scheme?