Jeff and his team's search for the wrecks of Mary, Joseph, and Neptune takes them further into uncharted territory. When an unusual artifact suggests a nefarious past for one of the ships, Jeff begins to suspect he may be on the verge of uncovering a field of stolen treasure.
Following the trail of a cache of precious gemstones, Jeff and the team move further beyond the breakers, in search of The Neptune. With stormy weather closing in, a puzzling find may lead them one step closer to a privateer's long-lost treasure.
A powerful hurricane forces Jeff's team into a secluded cove, where they investigate The Lombrac, an 18th-century ghost ship; as the divers recover clues from the depths, Jeff zeroes in on the site of a 300-year-old mystery that may be solved.
With time running out, the team returns to Le Chameau for another attempt; the team must make one final push to find the Chameau's remaining fortune and complete the mission Jeff's father started decades ago before time runs out.