A civic volunteer attached to Bansdroni police station was injured when a man allegedly attacked him with a sharp weapon after police went to rescue his father early on Sunday.
Officers said the father had made a distress call to Lalbazar pleading with the cops to save him from his son who he said had injured him.
The accused also allegedly damaged an ambulance, which the police had taken along to rescue his father, when cops tried to get hold of him.
The man has been arrested and the father and the civic volunteer were admitted to MR Bangur Hospital.
The police said the man seemed to be suffering from some mental ailments. He had been arrested in May 2012 in a case of murder in Regent Park and was out on bail, they said.
The address in Bansdroni's Bramhapur where the police arrived on Sunday morning is a sprawling property with huge iron gates, but lying in neglect. Some residents of the locality told the police that the father once owned a film studio in Bansdroni.
"The father called the police helpline, 100, early on Sunday. He said his son had attacked him and he was bleeding. He sought our urgent help," said a senior police officer.
"A police team reached the spot around 7.15am. When the team members went to rescue the elderly man, his son attacked a civic volunteer with a sharp weapon. The volunteer was injured."
"The son had confined the father in a room and locked the door from outside. He was standing guard at the door," the officer said.
One of the cops called Bansdroni police station and sought reinforcement, including a team from the disaster management group (DMG) of Kolkata Police.
By the time DMG personnel arrived, the police overpowered the son, who had by then smashed the windowpanes of an ambulance that was taken to the house to transport his father to hospital.
"The son has been arrested under various sections of the Bhartiya Nyaya Sanhita. It seems he is suffering from some mental ailments. We will check whether he is undergoing any treatment," the officer said.