John was caught by demons after attempting to con them with a fake Colt. Sam and Dean learned of his status and location from Azazel's daughter. They both decided to rescue their father, as well as bringing the Colt with them.
Sam and Dean infiltrated the apartments by sounding a fire alarm. Once the firemen arrived, they both took on suits and posed as firemen in order to enter the building. With the use of an EMF detector, they located the room where demons were keeping John. They were attacked by two humans who were possessed by demons. Sam and Dean fended them off by locking them inside a closet and pouring salt on the door. Once inside, Dean checked on his father. Sam wanted to be sure John was not possessed and so splashed his father with holy water. As there were no reaction, and as his father began to wake up and asked Sam why he was splashing holy water, the brothers were convinced John was not possessed and unbound him.
Once John was freed, two more demons appeared from the apartment entrance and proceeded to make their way into the building. The Winchesters escaped through the fire exit and poured salt behind them to prevent other demons from following.
When the Winchesters reached the street, they were attacked by Tom. Sam was pinned by the demon and was getting beaten up badly. Dean momentarily put John to the side of the street and used the Colt to shoot Tom, thus killing the demon.
Sam and Dean escaped with their father and fled into a cabin in an unspecified woods while waiting for their father to recover. The Colt had two bullets left. With the four demons trapped, Azazel's daughter exorcised and Tom dead, there were no known threats to the Winchesters aside from the Yellow-Eyed demon himself.