How does the author use the sea as a symbol in the novel, The Last House Guest?

The sea is symbolic of both life and death. When it is calm, it is beautiful and enjoyable. However, it can turn tempestuous at any time, without warning. The sea also swallows secrets then reveals them at its will. In the novel, the sea swallows Sadie's body after Collins dumps her into it and reveals her soon after - something Collins probably did not count on. The sea can also represent emotional balance, which can change like the turn of the tide. There are moments in the novel where characters' emotions quickly shift from being calm and collected to being angry. Avery's anger comes forth in an uncontrolled burst when she has her fight with Faith, and Parker's aggression comes out in his confrontation with Collins, breaking his constructed aloofness.