Pex's actions earned him the nickname "scaredy cat". Other than the Caretakers, he was the only inbetween in Paradise Towers. Ashamed of his cowardice, Pex began exercising and learning martial arts to improve his physique. He was soon capable of great feats of strength and began patrolling the corridors, announcing he was "here to put the world of Paradise Towers to rights".
Pex met Melanie Bush when he broke down the door to Tilda and Tabby's home. They told him to leave and Mel also left. She was unimpressed by a demonstration of his prowess; he only destroyed things, rather than righting them. Pex decided to accompany Mel to "the pool in the sky", where she had arranged to meet the Seventh Doctor.
While in the Fountain of Happiness Square, Mel questioned Pex about how he came to be in Paradise Towers. He lied and told her the power to protect had been invested in him by those he was not allowed to name.
They ran into the Blue Kangs, who told Mel the the truth of how he had come to Paradise Towers. Mel left Pex to be taunted by the Kangs. However, Pex followed Mel and again burst into Tilda and Tabby's home. He found they had tried to kill and eat Mel, but Tabby had been killed by a cleaner. Tilda threw a knife at Pex. It missed narrowly and she too was killed by a cleaner. Mel thanked Pex for saving her and they again set off for the pool.
They found a lift, but upon using it, found themselves victims of the cleaners, who were pressing the buttons up and down the shaft so that the lift was constantly in motion. Pex kicked the console and the lift plummeted to the basement. A cleaner was waiting, but Pex had the lift head up again, straight to Floor 304 and the pool.
Pex was unnerved by how clean the area was and sat on the side while Mel swam in the pool. When she was attacked by an aquatic cleaner, Pex lent her his gun with which she destroyed it. They were joined by the Doctor, the Red Kangs and the Blue Kangs. All of the Kangs began taunting Pex, so he volunteered to lead Kroagnon to the Doctor. The Kangs then recognised his bravery.
Pex told Kroagnon that he could lead him to the Doctor and his offer was accepted. However, Kroagnon scared Pex and he did not follow the Doctor's orders to delay their arrival as much as possible. The trap was not ready. The Doctor tried to push Kroagnon down a lift shaft, but wasn't strong enough. Kroagnon began beating the Doctor to death. Pex took a stick of explosive and threw himself and Kroagnon down the shaft. The resultant explosion presumably killed them both.