Fletch spies on Blackbeard at the hidden cave and pilfers what Lowe later identifies as a glass bulb detonator capable of causing great explosions. In other words, Blackbeard's hoarding bombs and, in Lowe's opinion, intends each one for the island of Jamaica - and scores of innocent people. This seals it for Lowe; Blackbeard must be stopped.
Meanwhile, Selima remains suspicious about Blackbeard's planned surgery despite Lowe's redoubled attempts to explain the integrity of his motivations. In turn, Blackbeard suspects Selima of capitalizing on the potential power promised to her in the event of his death - does she want him dead? Emotional from his accusation, she concedes to the surgery against her better judgment.
After Rose once again rejects Nenna's payment as a fulfillment of her debt, Nenna sneaks back to her buried treasure chest. Only she's not alone - Rose appears, smug with success and ready to seize all of Nenna's valuables. Except when Rose opens the chest, it's empty - and Nenna slits her throat, shoving Rose into the makeshift coffin and burying her while she coughs out her last breaths.
Lowe makes one important stop before implementing his secret plan - Kate. He steals a private moment with her and confesses in earnest to the truth: he is an English spy sent to assassinate Blackbeard. As she reels, he assures her of his new intentions - save Santa Campana from its crazed leader and, most of all, take Kate with him. Unfortunately, Kate understands loyalty better than Lowe and she attempts to injure him in lieu of spreading the news of his betrayal. This forces Lowe to subdue her to the point of unconsciousness and make his escape.
But Balfour overheard the conversation and he rushes to Selima with the news. She sends pirates scouring across the island to find Lowe and they all return empty handed... while Lowe takes Blackbeard hostage in the hidden cave. He holds the commodore at gunpoint, intending to make an exchange that will leave Blackbeard with the Governor of Carolina and ensure Jagger's removal from his post in Jamaica, thus saving lives on both islands. Blackbeard takes offense to the plan and knocks away the gun, sparking an intense, bloody duel that leaves Lowe at the commodore's mercy and a crowd of hungry pirates awaiting his demise. Instead of killing the beaten surgeon, Blackbeard asks Rider and Selima for their opinion - while also confessing that he knows of their affair. They save face by allowing Lowe to live... and Blackbeard's surgery to commence.
And so it does that night, with the commodore's screams filling the air as Lowe twists the trephine into Blackbeard's skull and drills through to the brain. They seal the quarter-sized hole and soon Blackbeard sleeps in his bed while Fletch joins Lowe outside to decompress. But Lowe deflects any congratulations for a successful surgery and makes a major admission - it was all a lie. His diagnosis, the cure - Blackbeard didn't need any of it. Lowe fabricated the whole thing as an excuse to sail to Jamaica and report back to Jagger.
The very same Jagger who continues his relentless torture of Antoinette in her asylum, now using Lowe's sketchbook as evidence that her ex-lover Edward Teach, aka Blackbeard, remains alive. She reacts with wild rage during each session, until a sudden comfort washes over her and she recites an encrypted rhyme. Jagger manages to crack the code and an epiphany results - the chronometer Blackbeard sold to the Spanish will lead the fleet not to pirate-free waters, but instead to a surprise attack from Blackbeard himself, the only one who knows where the Spaniards (and their immense treasure) will be.
Back on Santa Campana, Blackbeard's post-surgery slumber comes to a frightening end as the most vivid of all his hallucinations joins him at the edge of his bed - Antoinette, pale and ghastly, baby cradled in her arms - and Blackbeard reacts with a terror more intense than the surgery that left a hole in his head.