Duane Ollinger believes there's a fortune of gold buried beneath his property in Utah. He's not going to stop until he finds the treasure, no matter the cost.

With an access tunnel to an underground cavern finally opened and a tantalising clue discovered, Duane's son Chad takes a risky dive into the flooded cave system.

Duane and the team search for new access points to the underground cavern system. But something lurking in the darkness forces everyone to re-evaluate their safety.

The team discovers mysterious ancient markings on a cliffside, and a mining shaft dug deep into the mountain that could lead them right to the gold.

Duane employs ground-penetrating radar to scan the land, leading to a mysterious finding. Trespassers prompt Charlie to increase security on the ranch.

As winter closes in and the digging season nears its end, Duane takes a final shot at getting into the underground cavern and uncovers a whole new mystery about the land.

The crew return to the ranch to strategize a new plan to get the box out of the underwater cave. And, Charlie investigates a mysterious death on the ranch.

The results from the radiocarbon testing are in, which will tell Duane if the box is Aztec or not. And, the men discover they are being watched by a high-tech camera.

When a windstorm ruins visibility in the water, Chad considers a risky blind dive to extract the box. Plus, intruders are discovered on the ranch.

Chad makes a huge mistake that could prove costly. Plus, a shocking discovery inside the box forces Duane to rethink everything.

Determined to get into the cavern, Duane explores new methods to find a dry entrance. Meanwhile, Chad takes to the skies in search of a natural opening.

After Duane makes a costly mistake, Eric and Chad finally discover what they've been looking for. However, the crew gets distracted by mysterious intruders.

After the crew drills into a dry cavern, they must devise a plan to protect themselves from poisonous gases. But trespassers threaten their progress.

As the crew explore the cavern, they are overcome by a deadly and invisible gas cloud. It'll take a complicated rescue mission to get them out alive.