For a three-act plot analysis, put on your screenwriter’s hat. Moviemakers know the formula well: at the end of Act One, the main character is drawn in completely to a conflict. During Act Two, she is farthest away from her goals. At the end of Act Three, the story is resolved.
Act I
The first act comprises Books I and II, and it's when the major storylines are laid down and the characters established.
Act II
This act's all about globetrotting: Achille to Africa and the Middle Passage (Book III); Walcott in North America (Book IV); and then Walcott moving through Europe and returning to North America (Book V). Put on your travel pants for this one.
Act III
Here—in Books VI and VII—we return to St. Lucia, witness a visit to hell, and generally see the various plots wind down.