Annabel's family is complicated (and diagrammed on the cover of the book). When she travels from New York to visit her father and his new family in Australia, she has one thought in mind -- to convince him to come back. She sees her new stepsiblings and stepmother as the ones who stole her father from her so, despite their initial friendliness, she is determined to be cool to them.
But, of course, this doesn't go as planned. Her father is happy with his new family in a way that he never was before, and she finds herself liking her stepsister, Lucy. But more difficulties are on the way -- while she was gone, her mother got remarried to the father of a boy in her class.