1 {scene: Port Royal, Jamaica}
1 Ponsonby: So how can I find the pirates if I don't know where they might be going, Governor?
2 Governor: The map they stole leads to a small island off the south coast of Antigua.
3 Ponsonby: Now if only you'd told me that before I left...
4 Governor: You'd have gone straight there and claimed the buried treasure for yourself.
4 Ponsonby: Well, true.

Antigua.

Captain Ponsonby is nothing if not mercenary.

---

2018-01-27 Rerun commentary: Unfortunately, Google Maps reveals that there aren't any small islands off the south coast of Antigua. Unless Montserrat counts.

There's also a tiny rock with a couple of trees on it inside Antigua's Falmouth Harbour, which is technically off the south coast, but that actually seems less likely than Montserrat, at least in my mind.

The next most likely interpretation of this lead is Guadeloupe, which is the next landmass south of Antigua, but that hardly qualifies as a "small island" as it's almost six times bigger than Antigua.

So either the geography of the Caribbean is still somewhat mysterious, with strange non-existent islands marked on maps, or the map the pirates stole is a deliberately misleading fabrication.