My Bones and My Flute - Edgar Mittelholzer

Only when he is on board the steamer halfway to their remote destination up river in Guyana does Milton Woodsley realise that there is more to Henry Nevinson's invitation to spend time with his family in their jungle cottage. Milton, an artist, thinks he has been invited to do some paintings for Nevinson, a rich businessman, and possibly be thrust into the company of their daughter, Jessie. But when the Nevinsons mention a flute player that no one else can hear, Woodsley begins to glean that there is more to their stay.