Plot hole: Ruthven is apparently bitter that he has been denied his chance of becoming an immortal vampire after Clara steals the map from him, which is why he attacks Eleanor. But why doesn't he just go to the island anyway? You don't need to be invited - Clara, Eleanor and Frank aren't. Having been there once, it seems highly unlikely he can't find it again - he's a naval captain, so navigation and observation are major professional skills for him. And it isn't hidden or magically protected - the local boatmen know where it is and are prepared to take people there, although they won't set foot on it themselves. He could quite easily have gone there without the map, entered the shrine and been turned into a vampire if that's what he wanted.