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.

With time running out, the team returns to Le Chameau for another attempt at its elusive stern. When a series of finds threatens to upend their plan, 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?