The Sinclair family is a very wealthy family. They own a beach house on an island off of massachutats. They go every summer with their cousins, aunts, and grandparents.
Durning Summer 15', something terrible happened. Shegot in an accident. She woke up half dressed and half under water. Now suffering from migraines. She was not allowed to go to the beach house Summer 16'. Instead she had to go to Europe with her dad.
After the accident Johny, Mirren, and Gat (Her cousins) ignored her and her emails. Cadence doesn't remember what happened and nobody will tell her. She finally get to go to the beach house in Summer 17'.
Cadence finally remembers what happened in Summer 15'. The Liars burned the Clairmont beach house to the ground.
After she remembers what happened, she goes to confront the Liars. Out of all 4 of them only Cadence escaped the fire.
Cadence realizes that she is the only one left. All her cousins died in the fire.