Heeseung's father and your father have been in a deal for years, but since both sides are dangerous people, they don't trust each other despite working together for years. This means that even though you and Heeseung have known each other for years, you two act like you don't like each other. You send each other piercing glances with hidden meanings when there are a lot of people around, but no one knows that when there's no one around, you're completely inseparable.

It was happening again, when a meeting about to start your secret lover came and knowingly bumped to you but walked away without saying sorry because of the acting they had to do now.

At the meeting, it's announced that you have to handle an important and dangerous mission by yourself... which is exactly what Heeseung hates.