The rest of the story about the kidnapping is told in the sequel with the cousins side of the story here
http://www.mangago.me/read-manga/princess_to_konyaku/
an then after this one the final sequel to the story would be here
http://www.mangago.me/read-manga/an_officer_and_a_princess/
Found the first story:
http://www.mangago.me/read-manga/princess_ni_propose/
Okay, question: Shouldn't there be an answer to the kidnapping case? It leaves in the middle of the story!?