Giulio, 23 years old is studying at the Università di Scienze delle Comunicazioni and, as film buff, is preparing an exam about Hitchcock. One day he is about to hire the DVD “Strangers on the Train” and chances upon a scene which grabs his attention: two young women (both in their thirties) but very different: Sasha, tall, dark haired, with an aggressive look whereas Federica, is shy, blonde and looks demure and they both want to rent the same film as him. This chance encounter would seem to indicate the beginning of a friendship. On leaving the DVD rental shop, which belongs to Andrea, a friend of Giulio’s, the two ladies exchange phone numbers. One night, days later, looking out of his apartment window Giulio discovers that the dark haired woman lives opposite. Giulio recognises the soundtrack of the rented DVD that the young woman is obviously watching. Her viewing is interrupted by the arrival of her mother with whom Sasha starts quite an aggressive argument. The day after she returns the film at the hire shop she sees Federica arrive and also rents “Strangers on the Train” after it was returned so quickly. Outside the shop Giulio looks on as Federica thanks Sasha on the phone. Both of them seem to have indeed become friends as Giulio, albeit remaining unseen, observes them meeting in the park. That same evening Giulio is woken up by a strangled cry. Sleepy as he is, the young man goes back to sleep only to re-awake some hours later because of noises from the street below including different police cars. He then learns that in the very building opposite a woman had been murdered: Teresa Zerbini, Sasha’s mother. This seems a brutal crime. And it is the beginning of nightmare which does not leave much room for a manoeuvre…