After the gang got a little pyromaniacal at the Mandibles' place, nothing's as it should be. Wally has suddenly turned into an eternal optimist, Vampire Dad wants to give the twins up for adoption, and Cheyenne has been acting awfully, well, hypnotized lately. Meanwhile, everyone in downtown Cincinnati is snotting and snuffling from a mysterious and deadly flu virus--and the ont larvae are quietly gaining strength underground.
Luckily, a suspicious stranger with a syringe shows up to give Wally a free "vaccination." (Now, there couldn't possibly be anything wrong with that picture, could there?)