The year is 1756 and Dr. Sabian Blake, a rich and privileged member of London society, is studying the night skies with his telescope looking for the scientific discovery of a lifetime. The sign he seeks is called Wormwood, a giant comet long foretold in a book called the Nemorensis. But Blake is as far from understanding the full details of his extraordinary book as he is its ancient origins and true purpose. As far as he can tell, the name of the comet is the only clue to its nature, the bitter herb wormwood. The night he spots the far off comet he sees that it is heading for Earth, and straight for the city itself.
The first portents of things to come are the packs of dogs, which go mad with bloodlust and horses stampeding in the streets. Who can blame his poor maid Agetta for hiding in the cupboard for fear and overhearing his conversation? But now she too knows his secrets and is drawn into the game. Outside the house spies lurk, watching and waiting, one of them has the peculiar trick of appearing and disappearing in the spookiest manner. Agetta's nefarious and grasping father wants to know how she can steal this priceless book without getting them all caught and hung.
Now the news is out several people are determined to get Blake's book: the mystery woman drugs Agetta and tries to murder Blake by creating a magical statue which is transported into his house to steal his book. But Agetta manages to survive the drugs and steal it by stealth. She hides the book at the haunted shop of the bookseller she has befriended but she has little idea of his true motives and the danger she is now in. The comet comes closer to earth and rains death and destruction onto London. The spy outside Blake's house now proves to be, if not an enemy, something of an ally to him. The true extent of his magical powers starts to be seen as he brings an unlucky man back to life who has been killed by a bullet in the chest. The final showdown is a magical battle at the bookshop.
This report prepared by Your'eRight