Vicky vs Mermaid

How do you catch a killer who can be anyone?
When in Cancun and Vicky sees the faceless body of a long dead girl wash up on the beach, she starts to get that old familiar feeling again. Who did this to her and why? and why is she hearing a voice in her head telling her it's not human?

She soon discovers that the Spriggan was the tip of the demon iceberg and that mermaids in real life are a lot less sweet than Disney would have one believe. Now she has to fight a girl that can punch a hole through a brick wall and used to be a viking. Lucky she's from south london.