Poison Island by Sir Arthur Thomas Quiller-Couch (1863 - 1944)

Mysterious old Captain Coffin not only has a wild story about a Honduran island where treasure lies, he has a map. But they must be wary because it also holds “a poison that kills a man and keeps him fresh as paint”. Nothing can hold Harry back from tagging along and meeting up with murder, intrigue, a collection of colorful characters, and a vociferous parrot. - Summary by Amy Gramour