Adam and Hoss put their lives and the Cartwright reputation on the line to help German engineer, Philip Diedesheimer, convince greedy silver mine owners and shareholders to use his innovative honeycomb support system to improve mine shaft safety and save miners' lives.
- The mines in Virginia City aren't safe. The depth and width of the silver veins can't be supported by the current form of timbering. When a mine collapse occurs in the Ophir Mine, Adam works with his good friend and mine foreman, Gil, to investigate. The Ophir owner, Andrew Holloway, has also hired an engineer, Philip Diedesheimer, to look into it. While in the mines, another collapse occurs trapping Adam and Diedesheimer and killing Gil. The two survivors are even more determined to find a solution. After much thought, and some arguement with Holloway, Diedesheimer comes up with the square set. It requires a lot of timbering, but has many advantages and nearly guarantees safety. But due to the additional lumber, none of the mine owners are interested and even accuse Adam of trying to find a way to make more money. But not one to sit back and accept defeat, Adam, Hoss, and Diedesheimer proceed to install the new square set in the Ophir. They test it by setting off a dynamite explosion near by. Unfortunately, all the mine owners have entered the mine to look at the new system. When their lives are saved because of the square timbering, they all agree to invest in the new system.