Broken Hero by Jonathan Wood

How’s a secret agent meant to catch a break? If it’s not a demi-god going through puberty, it’s a renegade Nazi clockwork army going senile. Or a death cult in Nepal. Or a battery-chewing wizard’s relationship problems. Arthur Wallace, agent of MI37—Britain’s agency for dealing with the supernatural, the extraterrestrial, and the generally odd—has to pull everything together, and he has to do it before a magical bomb tears reality apart…