Death Sets Sail by Robin Stevens

 Daisy Wells and Hazel Wong are in Egypt, taking a cruise along the Nile. They are hoping to see some ancient temples and a mummy or two; what they get, instead, is murder.

Also travelling on the SS Hatshepsut is a mysterious society called the Breath of Life: a group of genteel English ladies and gentlemen, who believe themselves to be reincarnations of the ancient pharaohs. Three days into the cruise their leader is found dead in her cabin, stabbed during the night. It soon becomes clear to Daisy and Hazel that the victim's timid daughter is being framed - and they begin to investigate their most difficult case yet.

But there is danger all around, and only one of the Detective Society will make it home alive...