Once upon a time, abbess Maria and sisters Arsinoe, Ourania, Agathoniki and Chrysovalanto lived calmly and peacefully in the monastery of Agia Theodouli. Until they discover a man's corpse in the sacristy and their lives turn into hell... The investigation of the case is undertaken by the experienced police officer, Miltiadis Sofianos, and his rookie assistant, Hector Tsakalakis, with orders to conduct the investigation in strict secrecy. Sofianos and Tsakalakis have the nuns as prime suspects and interrogate them. Strangely enough, none knew the victim and none saw anything suspicious on the night of the murder. However, evidence soon comes to light that indicates the opposite: one of the nuns secretly put the victim in the convent and then murdered him.

The arrest of the abbess causes fear and disturbance to the rest of the nuns, who begin to doubt her innocence. The police pressure the abbess to admit her guilt, but she denies any involvement in the murder. Fearing possible condemnation, she decides to take fate into her own hands and begins a secret investigation with the aim of solving the murder herself. At the same time, Karaiskos and Stamatis also start an investigation to find out what happened to Petros. Meanwhile, Sofianos and Tsakalakis discover a new clue that proves that one of the nuns gave a false testimony. On the night of the murder, she left her cell and had a suspicious date outside the monastery.

The discovery of the theft of the painting further complicates the investigation of the abbess who is asked to solve this case in addition to the murder. At the same time, Father Fanourios suspects that something serious has happened in the monastery and decides to follow the movements of the nuns to find out. Sofianos and Tsakalakis examine the closed-circuit video of the morgue and approach the tracks of Karaiskos and Stamatis, while the abbess manages to find out the address of the victim's apartment. There, an unpleasant surprise awaits her that will endanger her life.

The consecutive absences of the Abbess from the monastery raise suspicions against Sister Arsinoe. The Abbess is forced to reveal her secret investigation and takes her along on the next mission. Sofianos and Tsakalakis use the findings from the forensic report and find out important information about Angelos' life. At the same time, Stamatis is afraid that the police will track them down and pressures Karaiskos to stop dealing with Petros' murder. A while later, one of the nuns is getting attacked inside the monastery.

The attack on the abbess leads Sister Arsinoe to the conclusion that the perpetrator of the monastery's crimes is among the nuns. Meanwhile, Karaiskos and Stamatis visit Agia Theodouli monastery trying to find clues that will lead them to the nun who has the solution to the mystery. At the same time, Sofianos and Tsakalakis come upon to a new revelation that overturns the facts so far: one of the nuns of Agia Theodouli has once been accused of murder...