Well written, though they stick close to their “formula,” Bellairs’s suspense-filled and entertaining mystery thrillers are the perfect reads for children who are progressing fast beyond their own second- or third-grade reading levels but may not be emotionally ready for the more frightening horror novels the older kids are reading. In fact, these are so good that many of the fifth- and sixth-graders who read nothing else but adult horror become huge fans of Bellairs’s work when introduced to him. There are many novels, and some of the best are The Trolley to Yesterday, The Vengeance of the Witch-Finder, and The Ghost in the Mirror.
From Valerie & Walter’s Best Books for Children (2nd ed.), p. 362:
THEMES: horror; mystery; adventure