In London in the 1930s, a bank robbery is reported at the same time a man reports a missing cat to the Invisible Detective. Two seemingly unrelated events, but both lead the Invisible Detective on a hunt through the London sewer system. When the Invisible Detective begins his investigation, he stumbles upon something so strangeso beastlythat it could be deadly. Meanwhile, in present day, Arthur Drake continues the search for his link to the Invisible Detective. And unfortunately, his search leads him to a face-to-face encounter with something beastly as well.