Mia Chang, Kieran's girlfriend and Gabbie's best friend, disappeared on the day of the accident in the sea caves in 2009, and her fate is a central mystery in the story.

Kieran Elliott is the only survivor of the accident in the sea caves in 2009, which resulted in the deaths of his brother Finn and others, and the disappearance of Mia and Gabbie.

Bronte, who is Liv's flatmate, takes an active role in investigating the disappearance of Gabbie Birch, Liv's sister, who went missing during the storm in 2009.

Verity Elliott is Kieran's mother, and she blames him for the death of her other son, Finn, who died in the accident in the caves.

Key family members affected include Kieran Elliott and his parents Verity and Brian Elliott; Liv Birch and her mother Trish Birch; and the Gilroy family, including Julian Gilroy and his sons Liam and Sean, all connected to the victims and survivors of the 2009 storm and cave accident.