De Horlogemaker Van Londen by Natasha Pulley

In Victorian London a timid telegraph clerk is jolted out of his quiet life when a reclusive Japanese watchmaker—maker of uncanny mechanical marvels—saves him from a violent plot and draws him into a tangled mystery of clandestine politics, hidden identities and strange coincidences; as their unlikely friendship deepens, secrets about fate, loyalty and the power of intricate engineering reshape both their lives and the city around them.