Who Wants to Marry a Duke by Sabrina Jeffries [Jeffries, Sabrina]

A past kiss with adorably bookish Miss Olivia Norley should be barely a memory for Marlowe Drake, the Duke of Thornstock. After all, there are countless debutantes for a handsome rakehell to charm beyond a young lady whose singular passion is chemistry—of the laboratory type. But Thorn has not forgotten—or forgiven—the shocking blackmail scheme sparked by that single kiss, or the damage caused to both their names. Now Thorn's half-brother, Grey, has hired the brilliant Miss Norley for her scientific expertise in solving a troubling family mystery. And the once-burned Thorn, suspicious of her true motives, vows to follow her every move.
For Olivia, determining whether arsenic poisoning killed Grey's father is the pioneering experiment that could make her career—and Thorn's constant presence is merely a distraction. But someone has explosive plans to derail her search. Soon the most unexpected discovery is the caring nature of the reputed scoundrel beside her—and the electricity it ignites between them .