“That old place may be full of rats, and if so, I’ve got an antidote on call.” Having passed the wall, we took our way to the house, taking care to keep in the shadows of the trees on the lawn when the moonlight shone out. When we got to the porch the Professor opened his bag and took out a lot of things, which he laid on the step, sorting them into four little groups, evidently one for each. Then he spoke:⁠—