It's hard enough for Scooby and the gang to crack the mystery of a Dickensian Yuletide ghost...but it's harder with "help" from Mystery, Inc.'s newest member: Harley Quinn! Harley's decided to try a new career as a ghost-busting detective-and when she swings that giant mallet, nobody's going to tell her "no." But the gang doesn't suspect the real reason for Harley's relocation: She's on the run after a "lover's spat" with The Joker-and Mistah J wants her back!