From The Perry Mason TV Show Book
When Adam Thompson tells his two nephews that a parcel of land will multiply five times in value when he develops it, he decides to test their honesty. He doesn't tell them where the land is. Instead, he locks a map of the parcel in his safe and sets up an infrared camera to photograph anyone opening the safe.

The next morning, although the safe is unopened, someone buys the land before Adam can. The buyer turns out to be Adam's foreman, who later is murdered. Because he had fought with the foreman shortly before the murder, Adam's nephew Harry (played by Bert Convy) is arrested for the crime and seeks Perry's expertise to get him off.