Attack of the Violet Vampire

Terror strikes! The Violet Vampire, a winged monster with sharp claws and glowing eyes, has been attacking all of London! Is it an advanced flying machine? An alien from another world? Could it possibly be a real vampire? And how are the notorious outlaws known as The Peterson gang involved with all of this? It's up to The MacDougall Twins and their good friend Sherlock Holmes to solve the case, with help from Inspector Lestrade, Scotland Yard, and a surprising special agent!