Rura-Tonga: Wreck of the Haruka Maru (2009)

From publisher burb:

A simple overflight of native fishermen in the South Pacific puts the characters on the track of a missing Japanese ship with a singularly deadly cargo. Can they discover the secrets of the Haruka Maru and put an end to its dangers?

The PCs begin on the Grumman G-21 seaplane Flying Fish, returning to Rura-Tonga from Port Moresby, New Guinea. It's a beautiful tropical paradise sort of day – brilliant blue skies, a bit of a westerly breeze, not a cloud to be seen as far as the eye can see.