Duke in Shining Armor by Hayleigh Mills

Far from a helpless maiden, Lady Catherine Davenport had her wits and a trusty derringer pistol at her disposal. As she journeyed to Switzerland to attend school, she did not plan to play the damsel in distress. Yet, even the most independent lady could use a bit of unexpected assistance when faced with the threat of highwaymen.
Enter Lord James Hastings, Duke of Pembroke, a man of wealth often maligned as a rogue or a rake. The truth, however, lay far from these labels – he was an industrious man of leisure, delighting in worldly pleasures as any man of his station might. Marriage was the last thing on his agenda until he crossed paths with the fiercely independent and intellectual Lady Davenport.
He becomes her savior in a turn of fate, offering her protection under the most extraordinary circumstances. He was able to keep Catherine safe from the highwaymen, but the real question remains: could he protect her from the danger he himself posed?