Jolly Good Day Scooby Doo! (2014 Animated Film)

Scooby and the gang head to London as they meet up with an old friend as they investigate the Dragon that King Arthur had slayed.

Characters:

 * Scooby-Doo (Frank Welker)
 * Shaggy Rogers (Matthew Lillard)
 * Fred Jones (Frank Welker)
 * Daphne Blake (Grey DeLisle)
 * Velma Dinkley (Mindy Cohn)
 * ??? (???) - the gang's old friend
 * The Dragon (Dee Bradley Baker) - King Arthur had slain the dragon with the power of Excalibur
 * Suspects:
 * Mr. and Mrs. ??? (Jeff Bennett and ???) - a married rich couple, ??? is a stern business man who says no comment and ??? is a rich woman who has interest in Daphne's fashion sense, Reason: ???
 * ??? (Phil Morris) - the Big Ben cleaner, he is stern and is very hesitant to warn the gang about the Dragon, Reason: ???
 * ??? (???) - a gothic British girl who knows a lot of sorcery, Reason: ???
 * ??? (???) - a skinny, yet slick investor who wants the tradable goods of London, he has 2 bodyguards at his side, Reason: ???

Clues:
???

Culprits:
???

Plot:
???