In A Darker Shade of Magic, V.E. Schwab introduces readers to a world where parallel Londons exist—each one with varying degrees of magic. The story follows Kell, a magician who can travel between these worlds. He is one of the last Travelers—rare magicians who can move between these different Londons. The four Londons are:

1. Red London, where magic is alive and well.
2. Gray London, which is devoid of magic.
3. White London, where magic is dying, and people fight to control it.
4. Black London, a forbidden world where magic consumed everything, and now it is nothing but a dangerous memory.

Kell, who serves as an ambassador for Red London, is caught in a dangerous situation when he smuggles a dangerous artifact from Black London. He meets Delilah (Lila) Bard, a pickpocket from Gray London, who forces him to take her on a dangerous journey between the worlds. Together, they uncover a conspiracy that threatens not only their world but all the parallel Londons.