After a long winter, the crew returns to Blind Frog Ranch to strategize a new plan to get the box out of the underwater cave. And Charlie asks for help to investigate a mysterious death on the ranch.

The results from radiocarbon testing are in, which will tell Duane if the box is Aztec or not. Then, the men discover they are being surveilled by a high-tech camera mounted just above the cave entrance.

When a windstorm ruins visibility in the water, Chad considers a risky blind dive to extract the box. But when intruders are discovered, Duane and his crew realize that time is running out.

Chad makes a huge mistake, derailing the operation to drag the box out of the cavern. But when they pull out some of the box's contents, they are shocked by what they discover.

Determined to get into the cavern, Duane and his team explore new methods to find a dry entrance; while Chad takes to the skies in search of a natural opening, Eric thinks the radioactive rocks found in the box might show them where to dig.

After the crew drills into a dry cavern, they must devise a plan to protect themselves from radioactivity and poisonous gasses; but as they get close to finally entering the cave, trespassers descend upon the ranch.

As Duane and crew explore the cavern they find themselves overcome by a deadly and invisible gas cloud. Complications with their rescue leaves them wondering if they will make it out alive.