Sometimes the path to true love is a walk on the wicked side.

Dr. Henry Jekyll has-almost-always lived by the rules. Hoping to improve society by separating a person's good and evil halves, Hal tests an experimental potion on himself. When the drug lowers his usual inhibitions, Hal crashes a high-class party, downs a strong drink, and propositions a sophisticated courtesan. All in the name of science, of course.

Calliope Finch needs only six more months as a glamorous mistress to earn enough to open the library of her dreams. So when Callie meets the awkward, bookish party crasher calling himself Mr. Hyde, she knows nothing can come of it. Not when his curious charm and unfailing honesty come at the expense of his bank account. All she can spare him is a kiss-and maybe one night.

Spurred on by their unwavering attraction, Hal and Callie soon become friends and scientific collaborators. But Callie's list of potential protectors is dwindling, Hal's potion might not be the solution he hopes, and a mysterious enemy is making mischief at every turn. With their goals slipping ever further from reach, Hal and Callie must put their minds and hearts to the test. Even if it means freeing sides of themselves they've long kept hidden.