Sweetest Little Sin (Series #4)

Lady Louisa Brooke has many suitors, but the only man for her is the wild and ruthless Marquis of Jardine. When Jardine suddenly abandons her after a long-standing liaison, he leaves her with nothing except the secret they share. Her future in ruins, Louisa recklessly accepts a mission from the head of the secret service and becomes embroiled in a perilous operation in which nothing is as it seems.

The Marquis of Jardine is determined to destroy the criminal mastermind who's sworn vengeance against all he holds dear. But when he hears that Louisa is to wed a dangerous enemy, Jardine is tortured by jealousy and fear for her safety. He tracks her down, only to discover that her mission collides with his.

Together, Louisa and Jardine must now foil a plan to betray the secret service and escape a diabolical revenge. But can they put the past behind them, and take the greatest risk of all—on love? Rated '3/5 - Open door' for steam/spice/heat level.