Harry was a young boy and a friend of Sam.
After showing Harry the train set Sam's dad had just finished, Harry and Sam started work on Harry's dad's set in Harry's garage, which had barely been started. They found a Cyberman in pieces in the garage, and slotted the metal and plastic pieces together until it was complete. They put it on a chair to watch them build their model train set, when the Cyberman's self-repair systems were initiated. The Cyberman compelled Sam to help it build upgrade equipment using the material in the garage. When the Cyberman tried to upgrade Sam, Harry used the train set to fly a train off the table, knocking the Cyberman off balance and causing it to fall into the live equipment and be destroyed. (PROSE: Going Off the Rails)