The Earl of Brass: Book One of the Ingenious Mechanical Devices, Jorgensen Kara

Eilian Sorrell is no stranger to cheating death, but when a dirigible accident costs him his arm, he fears his days of adventuring are over. As the eldest son of the Earl of Dorset, Lord Sorrell knows he will face a bleak future among Londons aristocracy unless he can escape. On a quest to return to his old life, Lord Sorrell commissions a prosthetic arm, but the craftsman isnt quite what he expected.
Fenice Brothers Prosthetics is in trouble. Hadleys brother is dead, and she is forced to pick up the pieces and finish what he started. When clients begin turning her away, she fears she will fail until she crosses paths with the enigmatic Lord Sorrell. In exchange for a new arm, he offers her a chance at adventure in the deserts of Palestine.
Beneath the Negevs sand lies something far more precious than potsherds or bones. A long lost crystal city has been found that could change Eilian and Hadleys world forever, but they arent the only ones who know its secrets. Will they make it out alive or will they, too, be buried beneath the desert sands?