Paul and Carla fell out of love when Clyde was younger. Paul ran off with her sister Melba and went to live in Germany. When Melba became pregnant in 2009, Paul ran again, this time returning to Clyde. Clyde showed him the attic in Sarah Jane's home and explained to him that in his free time, he helped to save the world.
Paul stole a Berserker pendant which made him go on an insane rampage through the city before Sarah Jane, Clyde and the gang made him take off the pendant, which returned him to his normal self. He was convinced by Clyde not to screw up his second chance at being a father when he was told about Mel's pregnancy. (TV: The Mark of the Berserker)