In a tense demilitarized zone between North and South Korea, a shootout leaves two North Korean soldiers dead and a South Korean soldier wounded. As the political ramifications threaten to unravel a fragile peace, Swiss-Korean military officer Major Sophie E. Jean of the Neutral Nations Supervisory Commission is assigned to investigate the incident. Amidst conflicting narratives from both sides, she begins to piece together a complex and emotionally charged story that suggests a much deeper connection between the soldiers involved than initially perceived.

Major Jean's investigation uncovers an unexpected friendship that had formed in secret between South Korean Sergeant Lee Soo-hyuk and North Korean Sergeant Oh Kyeong-pil. As she delves deeper into the soldiers' clandestine interactions, she faces mounting pressure from both governments to settle on a politically expedient resolution. Her quest for the truth forces everyone involved to confront their own perceptions of enemy lines, loyalty, and the boundaries that divide them. What started as a straightforward inquiry evolves into a poignant exploration of humanity amidst divided loyalties and nationalistic fervor.