When Marion finally gets the chance to babysit her little sister, she finds that the task is harder than she expected, especially when she gets called to the Critter Club to help with a stray cat and must bring Gabby along.

Jimmy Bishop likes crime fighters, vampires, and dogs, and he does not care for his new babysitter, so he is delighted when his new dog, Abby--who sleeps during the day, and grows huge fangs at night--turns out to be a crime-fighting, vampire dog, who also does not like the babysitter.