City of Light & Steam by Lexi Ostrow

Twelve years ago the Great Guilds put aside their rivalry and attempts for world control when a plague turned the sick into blood-thirsty beasts. Steam and Electricity no longer rivaled for world domination, but collaborated on tools to save their world. That ended when betrayal struck both Guilds, leaving them to fight the war separately.
Elise Nightingale was thrust into leadership of the Steam Guild when a ruthless vampire attack left her father and older brother’s dead. She was unprepared, and turned to the leader of the Electric Guild, Christopher Abbott, for help. On her way, she was attacked and left for dead.
Benjamin was smitten by the beautiful woman he found laying in the street just outside the guild mere feet from his Guildmaster. Posing as the head of the Electric Guild, he wooed her as best as he could, lying his way through things. Their love helps them to put aside differences and create great marvels, until she learns the truth and terminates the alliance.
As the vampires announce their claim to London, Elise and Benjamin will have to unite the guilds once more, or allow their city to fall. Their feelings must come second in the race to save London, but the lies of the past may destroy their future.