The killer leaves Tunisia believing they have disposed of the detective duo and Sarah Bedford after their car explodes. But luck seems to be in for Bernie and Robin, who smuggle Sarah back into the country as they try to figure out who could be behind the killings and why. Realizing the connection has to be the S.S. Mermaid and it's sinking, they track down Bernie's eccentric cousin Looby, who has an archive of old newspapers, to find out more. And their digging leads to an unexpected avenue as they discover the identity of the "seventh man" in the affair of the S.S. Mermaid. But just who is it behind all the murders?