I'm a believer in peanut butter bait for a Victor trap. Poisons work, but then you get to smell the dead rat for nearly a week because it died between the walls of your dwelling.
It can get in and out of the room somehow. Find the hole and plug it with steel wool. They won't chew through that.
It can get in and out of the room somehow. Find the hole and plug it with steel wool. They won't chew through that.