Ten Little Witches — Paul Ruditis

An Other Realm Halloween party
...for mortals? When Harvey Kinkle gets an invitation, he's told he can bring one witch -- and what better witch to party with than Sabrina? But even Salem, the master of dastardly tricks, can't figure this one out; so Sabrina agrees to accompany Harvey. After all, she can't let him go alone to the Other Realm. In true Other Realm form, this is no ordinary Halloween party. The mysterious host is nowhere to be found, and the motley crew of partygoers is disappearing one by one. Sabrina doesn't know who would ruin a witch's favorite day, but she's determined to get to the bottom of this mystery...before she's the last witch standing.