Jacob Marlin was the ghost of an evil serial killer and the main antagonist of the Horowitz Horror story Bath Night. Jacob was famous in his time in the late Victorian era, and often targeted women. Jacob would make a hobby of taking young women home, presumably raping them, and then slitting their throats in his bath, causing it to be stained with their blood. Jacob thoroughly enjoyed his work. His main weapon of choice was an axe. He was later arrested, imprisoned, tried and executed for mass murder. This was not his end, because his ghost returned from the Underworld and sought to continue his work, in the hands of whoever owned the bath. Jacob's bath, named the Marlin Bath, was sold to an antique's because of its gory history. Isabel's parents didn't know of its history because the shady shopkeeper didn't tell them. Isabel suspected the bath was odd the moment it was installed but she tried using it, and then suddenly it would play tricks on her, such as baking hot water turning freezing cold the next moment, then it filling up with blood in the mirror. Soon the supernatural events became more disturbing because the mirror showed Jacob himself walking down a corridor into her world. Soon Isabel went to the antique owner who told her of the bath's history. Isabel was revolted and when Jacob laughed at her in the mirror, she vowed to destroy the bath forever. She took an axe to it and destroyed much of it, but Jacob came into the mirror and walked out of the mirror, into the room, and tried raping her, but he vanished when her father opened the door.

Her father deemed Isabel mad because of the way she had been laughing maniacally and smashing the bath with an axe, so he and his wife sent her to recover in a hospital. Later, when her father was lying in the repaired bath in hot water, he thought over all the bullying he had experienced at school. He was implied to have been possessed by Jacob Marlin, because he decided he would go out and get an axe the next morning.