The play was further notable for being the closest the Quarks have ever come to returning to performed Doctor Who since The War Games. Though never heard, the Quarks are essentially the MacGuffin of the story and are mentioned at least once in each episode. From the Doctor and Mel's perspective, the events of Flip-Flop were merely a side-trip from their current "mission" to defeat the Quarks aboard the space yacht Pinto.