1885, East London

Abigail and Gideon are under siege. Noxious fogs have been bringing their clinic waves of indigent patients with inexplicable symptoms, telling wild tales of a demonic presence in the fog. If that's not enough, someone wants the clinic for themselves, and they're using the force of law to get it.

On the other side of town, heiress Meg Eisenstadt and her brother Nat live a life of well-intentioned aimless luxury. She dabbles in social justice causes and he pursues alchemy. And in a secret lab in the depths of Whitechapel, disgraced physician Jin Wylie attempts to rebuild his shattered life by performing dubious research for a shadowy cabal.

They live in separate worlds on different trajectories until the mysterious fiend in the fog brings them together.

Abigail and Meg discover a shared passion for social justice, and for one another. But where does that leave her plans with Gideon? And what of the future of the clinic? Gideon has his own monster. Can he keep it in check without Abigail's constant presence? Does Dr. Wylie's research hold the solution to Gideon's problems, or is it the cause of them? And could Nat's own dabblings be the key to defeating the vicious killer in the fog?