The correct answer is C. into.
The preposition “into” is used to indicate movement from the outside to the inside of a place or object. In this case, the enemy’s camp is a place that is dangerous to enter. The preposition “into” accurately reflects the fact that the speaker is entering the enemy’s camp from the outside.
The other options are incorrect because they do not accurately reflect the speaker’s movement. The preposition “through” is used to indicate movement from one place to another through a third place. In this case, the speaker is not moving through the enemy’s camp, but rather into it. The preposition “on” is used to indicate movement on the surface of something. In this case, the speaker is not moving on the surface of the enemy’s camp, but rather into it. The preposition “at” is used to indicate movement to a specific location. In this case, the speaker is not moving to a specific location in the enemy’s camp, but rather into it.