From amazon.com:

The only discernable bond in the relationship of brothers Mark and Mike Trevelyan is their fascination with the sea and its secrets. When Mike hears of his brother's death, during an expedition to a remote Pacific atoll, the circumstances are suspicious enough to force him to investigate, and when he is the victim of a series of violent attacks, his search for the truth becomes even more desperate. Mike has only two clues - a notebook in code and a lump of rock - enough to trigger off a hazardous expedition and a violent confrontation far from civilisation.

First published 1984
Fontana/Collins 1985

This Bagley's book is now available at the airport's Book Swap, thanks to the courier! With the book I'm participating Chania's 'Vapautusten vuosi 2016' release challenge.

Enjoyable reading moments!