When she was eight-years-old, Holly was out with her parents Mr and Mrs Hills and witnessed them being murdered by a hitman nicknamed "Porkman". Following their deaths, she was taken in by family friends, the Johnson family.
During the Combine's occupation, Holly became part of the resistance in City 14. She was abducted by the G-Man in order to be used as leverage against Nathan Johnson, on the orders of Wallace Breen. She was held prisoner at the citadel which resulted in Nathan rescuing her. However due to Nathan annoying Wallace Breen, Breen allowed the pair of them to leave, much to G-Man's annoyance.
- Mr. Hills (Father) (Deceased)
- Mrs. Hills (Mother) (Deceased)
- Paisley Hills (Younger sister) (Deceased)
- Gillian Hills (Younger sister)