Harold T. Martin III is a person who got in trouble with the law because he had access to secret government information and he took it without permission. This is a big no-no because the information he had could help bad guys who want to hurt our country.
Think of it this way - imagine you have a secret box with all your favorite toys that you don't want anyone to touch. Now, Harold T. Martin III had a secret box with important secrets that he wasn't supposed to take but he did anyway. This made a lot of people angry because he put our country in danger.
So, the grown-ups in charge of keeping our country safe had to investigate and put Harold T. Martin III in jail to make sure he doesn't do anything like this again. It's important to protect our secrets so that we can stay safe and happy.