The Mystery, Inc., gang has their hands full already with a Christmas ghost mystery in this week’s Scooby-Doo Team-Up #21—and then Harley Quinn decides to join them as well. Here’s the executive summary:

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!

The comic comes out in comic shops on December 28. Enjoy!