After playing the adventure some useful advice for Keepers:
There is an error in the PDF of the adventure:
The pre-gen character Maurice Lavalle has a character Claudette Petit named as his cousin as a pillar of sanity - it should say it is his aunt ( in our game, for a couple of hours, our player therefore thought he had an aunt AND cousin on the island as pillars of sanity until I worked out where the problem was ).
Other Keeper advice:
Overall I think the adventure is good but it could really do with an edit to make it much easier to assimilate for the Keeper.
Things that are not stated obviously enough but just sort of sneak up on the Keeper as they read the whole adventure:
1) Claudette Petit has a husband! This really is not stated at all but you have to work it out from the surnames of Claudette and a corpse!
He is Pierre Petit
At some point during the current shepherding run he broke off from the other 2 male ( cult ) shepherds to go to Mt Lyall ( probably to try to foil the cult ).
He was captured and thrown off the cliff where the adventurers should find his body once trekking.
Therefore if you have Leon and George come back and meet the adventurers in the homestead before "The Frenzy", Claudette should be worried as to why Pierre is not with them.
2) The De La Rues have a ridiculous amount of TNT on the ship but no reason is given in the adventure write-up.
When players discover this, one of the obvious questions of the De La Rues is "Why?"
Make sure you have some sort of excuse ready ( or tone down the amount of dynamite - the players can't carry much anyway once trekking, as they need to carry survival equipment ).
3) You absolutely must make yourself a Keeper-only map with the following marked on it:
The homesteaders' settlement quad
The ruined German observatory
Mt Lyall ( and the Black God's shrine there )
The Black Altar
Pierre Petit's body
The slaughtered sheep mess
The cave with the dessicated body
You can use the 2-piece black and white map in the PDF but stick the 2 pieces together ( they join left-right with the right piece a little higher ) and find/decide where all the above are on the map and mark them on. It is WAY too hard to free-form this sort of thing in play once the players want to know trekking distances and times etc.
Be prepared with strong knowledge of distances and trekking times.
Finally I had 3 players use 2 pre-gens each - this is pretty mind bending for the Keeper as each pre-gen has some sort of positive or negative relationship with other pre-gens.
If you also have three players and want to make sure each player has a relationship with both the other players then split the pre-gens into the following pairs:
Prof Lederman & Anita Desmarais ( have Anita married to Marc-David )
Marc-David Desmarais & Lt.Carlise Bullard
Maurice Lavalle & Dr Waechter.
Make sure you have some sort of diagram or aide-memoir on who hates/likes who.