In this episode, Mark and Sophie finally reveal the details of the story of how they traveled into the future to discover a race of subterranean creatures. After that, they traveled into the past, got rid of the annoying bugs flittering around and rode the sound of thunder back to the present.
After that epic tale, they also find the time to talk about the time-tastic series of books: The Chronicles of St. Mary's.
Just don't ask them to explain Primer.
Long may Richard III reign.