My Girlfriend Is an Agent (2009) on Netflix

Plot summary

A Russian organized crime group has taken an advanced bio-chemical weapon out of Korea, helped by a corrupt Korean scientist. Two agents are the only hope of stopping them. Ahn Soo-ji is a veteran who works at home and is trained in martial arts and fencing. Lee Jae-joon is a rookie who works abroad and leans on analysis rather than fieldwork. Both goof up on the job. Coincidentally they are dating, and neither knows each other's secret identity, which makes the relationship an ill-fated one. Each takes on the mission while working behind the other's back, unaware that they are chasing the same enemy.