The Deadly Isles
Plot intro from Wikipedia:
A young scientist with family ties to a vast fortune survives a murder attempt by a stranger while working in French Tahiti, and allows the assailant and the police to believe the attempt was successful. Incognito, he follows the would-be murderer aboard an island-hopping passenger/cargo schooner bound for the Marquesas, intending to find the man out. (Wikipedia, accessed 1 April 2019)
The time had come when he must leave Tahiti. Luke felt mingled anticipation and sadness. Out in Teahupoo the world was far away, isolated by a quality far more elemental than miles. Never again would he live so close to water and air and sunlight; his friends the Tefaataus, the Vaita’ahuas, the Himeas, their cousins and aunts and uncles would gradually forget him; gradually he would forget the songs and his few words of Tahitian. At Teahupoo the days passed slowly but the months slid by with disturbing ease. A man tended to lose contact with the world. The real world? Perhaps, perhaps not: Luke wasn’t sure. Still, more and more of late he had known small pangs of guilt. Perhaps someday he might return, but more likely not. The risk of anticlimax would be too great...Luke suddenly became aware that, without conscious deliberation, he had decided to meet the Dorado in the Marquesas. Armand could look after his belongings until he returned to Papeete.