In 1952, during the Panmunjom negotiations, the ownership of L Highland directly affected the demarcation of the ceasefire line. In order to obtain more favorable results, the North and the South launched a new round of bloody competition around L Highland. At this time, the captain of the Korean Crocodile Squadron on the front line was shot dead by his own pistol. At the same time, the family letters of the North People's Army soldiers were secretly sent through the Korean postal route. The South Korean side suspected that there was a traitor on the front line of the highland, and sent Lieutenant Jiang Enbiao (played by Shin Ha-kyun) of the investigation department to accompany the new captain to the Crocodile Squadron. At this time, the Crocodile Squadron was actually controlled by Lieutenant Jin Xiuhe (played by Gao Xiuxiu) and Captain Shen Rirong, Jiang Enbiao was surprised to find that Jin Xiuhe, who was once full of bookishness, had now become a tough fighter, and the Crocodile Squadron, which seemed to have lax military discipline, had amazing combat effectiveness in actual combat. Jiang Enbiao experienced a tug-of-war battle for the highlands with the Crocodile Squadron, and he finally accidentally discovered the clues of the Crocodile Squadron's "collaboration with the enemy"...