When Derpy Hooves shows up at the wrong time, an unfortunate time traveling mishap sends Twilight Sparkle, the town's librarian to an untimely early grave. Now stuck in the Pre-Equestrian period, Derpy and Rainbow Dash must fend off a slew of terrible titanic creatures.

Will Dash ever be able to forgive Derpy Hooves of what she's done? Will Derpy finally be able to do something without completely screwing it up? Will the two displaced Pegasi ever be able to make it home? Is there a lesson in friendship to be found in all of this?

The answer to these questions and more lies in the story "Of Derps and Dinos".