57 Gresham Street is the most incendiary building in London.

Upstairs, unconventional chemist Emmeline Starling uses combustion to solve scientific mysteries. Downstairs, buttoned-up children’s book printer Robert Vane tries very hard not to panic when the ceiling catches on fire. And when these two opposing forces are contained within one small building? Explosions are just the beginning.

After two years of putting up with Robert Vane’s scowls, his precious rules, and the infuriating cleft in his chin, Emmeline has seized upon a solution to the problem of sharing 57 Gresham: she’s purchased the entire building. Her attempt to remove Vane is thwarted, however, when Em and Robert uncover the theft of one of Em’s most dangerous compounds.

Soon Em and Robert are on the run together, chasing a ring of industrial spies who mean to use her discovery as a weapon. From a ship to an island to a foundry in Wiltshire, Em and Robert keep finding themselves trapped together—and close proximity transforms their sparks into a conflagration. For two passionate people who’ve always been at odds, explosive chemicals are nothing compared to the biggest risk of all: falling disastrously, catastrophically in love.