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
Captain Delano doesn't have a care in the world as he chills out on his boat, the Bachelor's Delight. When a ratty-looking ship pulls into his harbor, he goes over to check it out and finds a starving group of Spanish sailors and slaves captained by Benito Cereno. Apparently, the ship got stuck in a storm and was hit hard with scurvy.
Act II
Captain Delano becomes increasingly suspicious of all the sketchy stuff going on aboard the San Dominick. He sees at least a couple of the slaves beating the Spaniards, as well as an old man who seems weirdly fixated on undoing a knot. By far the strangest, though, is when Benito Cereno gets a shave from his right-hand man, Babo. Babo accidentally slices Cereno when he's about to give more details about the storm episode.
Act III
Captain Delano is about to peace out and leave the creepy ship for good when Benito Cereno basically throws himself at him. Babo tries to stab his "master," making Delano realize that the relationship might not be so hunky-dory after all. Delano sics the Bachelor's Delight on the San Dominick after finally figuring out that the slaves took over a long time ago. After taking the San Dominick back for the Spaniards, Babo and the rest of the slaves are put on trial and Babo is executed. Cereno can't hold out for much longer and dies right after Babo.