When Scott, Jack and Emily rescue a drowning man from the waves they are keen to hear his story, but their new friend can’t remember his own name, let alone how he came to be stranded at sea! Who is the mystery man? Why did he come to Castle Key? And was his drowning an accident – or attempted murder?

The friends are on the case – with enthusiastic assistance from Drift the dog – determined to find the truth and solve the mystery of the drowning man.