Kell is one of the last Antari—rare magicians with the ability to travel between parallel versions of London. There is Red London, vibrant with magic; Grey London, where magic has faded; White London, ruled by power-hungry rulers; and the forbidden Black London, destroyed by the dangerous force of magic itself.
Officially, Kell serves as an ambassador between the Londons, but he secretly smuggles forbidden artifacts between worlds. When a dangerous object from Black London falls into his possession, he becomes the target of powerful enemies. Joined by the daring thief and aspiring adventurer Delilah Bard, Kell embarks on a perilous journey to prevent a magical catastrophe that could threaten every world.