In Traverse City, Michigan, Marty Lagina, Alex Lagina, and Craig Tester meet with side-scan sonar experts and commercial divers Mike Roberts and Dave Delaney, who have over 50 years of combined experience in underwater visualization technology. Roberts and Delaney report that during a previous dive off the coast of Oak Island at approximately 57 feet, they found what they are convinced is a wreck of some kind on the ocean floor. The object appeared and then vanished under shifting bottom sediments in subsequent visits. They plan to return with higher-resolution side-scan sonar equipment and sub-bottom profilers, which send sound pulses that penetrate layers of sediment to create three-dimensional images of objects below the seafloor. Marty agrees to collaborate, noting that the island's shoreline has changed dramatically over the centuries and that the waters of Mahone Bay once lay along major European trade routes during the height of piracy.
On Oak Island, Rick Lagina and Fred Nolan conduct a second joint drilling operation, this time targeting a site just north of the swamp that Nolan calls the old well. While doing survey work in the swamp years earlier, Nolan discovered a depression covered by one to two inches of slate that produced a hollow sound when probed, suggesting an underground opening. The site sits on land once owned by Anthony Graves, a mysterious 19th-century property owner known to pay his debts with ancient Spanish silver coins. Using a three-inch coring bit, drillers Harold Fraser and Jason Pike from Logan Drilling take samples every six feet as they descend through slate bedrock. Unlike the porous anhydrite on the eastern side of the island, slate does not form natural voids, meaning any cavity would almost certainly be man-made.
At 106 feet, the drill core stops matching, and between 106 and 111 feet no core material comes up at all, indicating a five-foot void in the slate. Nolan is visibly elated, repeating "five feet of void" as he examines the core samples. Rick calls Marty to share the news. Marty remains characteristically cautious, noting that no human artifact came up with the core, but agrees the finding is exactly what they were looking for and worth further investigation. While not yet definitive proof of a man-made structure, the discovery represents the first time drilling on Nolan's property has produced evidence consistent with an underground chamber or tunnel.
Jack Begley, Alex Lagina, and Charles Barkhouse travel to the Bedford Institute of Oceanography in Halifax to consult with oceanographer Dr. Bob Courtney about bathymetric data from the waters around Oak Island. During the visit, they also follow up on Fred Nolan's description of a timbered wall he observed between the swamp and the beach: sawn square timbers stacked one atop another, extending down 12 feet and spanning approximately 12 feet in width. If confirmed, such a structure would be strong evidence that the swamp is man-made. Dr. Courtney shows them bathymetric maps revealing that Oak Island's south shore once extended roughly 300 feet further out than its present position, with erosion having dramatically reshaped the coastline over the centuries.
Roberts and Delaney deploy their side-scan sonar off Oak Island's south shore and discover a strikingly anomalous feature on the seabed: a triangular rock with what appears to be a perfectly inscribed triangle on its surface. Dr. Courtney examines the data and confirms he cannot explain the feature naturally, noting it is at a depth that could have been exposed centuries ago before shoreline erosion submerged it. The triangle appears to point toward the stone triangle discovered by Frederick Blair on the island's south shore in 1897. The team plans a dive the following day to put eyes directly on the object.
