If the viscount falls / Sabrina Jeffries.

Enhanced descriptions from Syndetics:

From New York Times bestselling author Sabrina Jeffries, the deliciously sexy fourth book in the Duke's Men Regency romance series--the first of which was called "a totally engaging, adventurous love story" ( RT Book Reviews , Top Pick).

The heir presumptive to the Viscount Rathmoor, Dominick Manton once had his heart's desire within reach--a bright future as a barrister and engagement to Jane Vernon, a wealthy baron's daughter. Then a shattering betrayal by his vindictive brother George snatched away Dom's inheritance and his hopes of offering Jane a secure future. Brokenhearted, and attempting to end their engagement without destroying Jane's reputation, Dom staged a betrayal of his own to convince her that he's not the husband-to-be that she thought.

Now George is gone and the viscountcy restored to Dom, since his brother's widow, Nancy--Jane's cousin and closest confidant--never bore an heir. But when Nancy goes missing, a panicked Jane calls on her former fiancé to track down her cousin. Dom knows the mistakes of the past may be unforgiveable--but now, entangled together in mystery and danger, will they rekindle a passionate longing that was never lost to begin with?