Cursed Under London by Gabby Hutchinson Crouch

Two strangers. Two Londons. Two hearts that won’t stop beating…In an alternative Elizabethan London, Fang awakes from his death to discover he is not quite human anymore. In fact, despite having somehow acquired the power of immortality, he’s also not quite vampire, zombie, werewolf or any of the other supernatural beings who roam the twin cities of Upper London and its underground counterpart, Deep London. A jaded traveller from the Ming Empire, Fang is desperate to find a way to reverse the spell and get on with being dead when he stumbles upon Lazare de Quitte-Beuf, a theatrical Frenchman who is afflicted with the same mysterious condition.

Thrown together by the curse they share, the two men set out to undo the strange magic that binds them. As they are drawn further into the shadowy world of Deep London, they find themselves at the centre of a dangerous plot. And when in grave danger, surely the worst thing they could do would be to fall in love, wouldn’t it?