When Marty gets ahold of a page from the diary of his sister, Erica, he expects to find a bunch of brags about what it's like to be the better Pants sibling. But what he discovers instead is something HUGE. Erica's written a secret about who or more accurately, WHAT Marty actually is. And though the page is torn in half, Marty, through his unique deductive skills, determines that he is undoubtedly a big-toothed, sharp-clawed, hairy-faced werewolf!...

Soon after Victorian messenger Barnaby Grimes is attacked by a huge beast while crossing London's rooftops, he becomes entangled in a mystery involving patent medicine, impoverished patients, and very expensive furs.

Looks at legends about vampires and werewolves in different cultures, their reputed appearance and behavior, similarities between the two creatures, and possible scientific explanations of the old stories.