The army has laid out an entire web of agents to detect the surreptitious activities of the enemy.

Answer: Option B

Hostile : showing or feeling opposition or dislike; unfriendly.
Secret : not known or seen or not meant to be known or seen by others.
Intriguing : arousing one's curiosity or interest; fascinating.
Foppish : (of a man) concerned with his clothes and appearance in an affected and excessive way.
Surreptitious : kept secret, especially because it would not be approved of.

Synonym of Surreptitious is Secret