Cathy ran away from home and got lost in the Nightside, but was saved by John Taylor in the first novel Something from the Nightside after was half ate by a man-eating house, which was used as a trap for John. After she recovered, she adopted John Taylor as her father and helps him as a secretary. She often goes out to party and collect information. She also decorated and manages John's office in a office district of the Nightside. Besides Cathy got permanent new stuff for John like a mobile or some super-futuristic computer.
Cathy is currently involved with Alex Morrisey, they kept their relationship a secret from John at first but he eventually found out and was not happy at first but he has come to accept them.