There is a great idea here, somewhat reduced by the execution as AG mentioned.
It also suffers from requiring the targets be oblivious and for a number of coincidences to occur to work - he has to be injured while closest to the generals, not his servants, queen, cooks or others. Seems like quite the stretch.
A great nautical adventure! This could even be the _starting_ point for a campaign - the PCs being survivors from a ship of political prisoners which was sold to the islanders, and the demon was not completely successfull in devouring all of the prisoners. The PCs wash up on an island and start off in a survival situation with little to no equipment.