Spoiler He is with the kidnapper, the kidnapper is the real Baek Saeon, his grandfather replaced him with this one (the one who is acting as Baek Seoan currently, actually this current one is the illegitimate child of the grandfather, but they raised him like his grandchild), real Baek Seoan's mother is also involved in this kidnapping case, and is the provider of the phone and gadgets to the kidnapper, Mr. Park the assistant here is also assigned by the mother only. (He thinks that this baek seaon has killed her sister in their childhood, but the reality is, the kidnapper baek seaon is the one that has killed his sister.
Credit. @VS-zp5ox
Spoiler
He is with the kidnapper, the kidnapper is the real Baek Saeon, his grandfather replaced him with this one (the one who is acting as Baek Seoan currently, actually this current one is the illegitimate child of the grandfather, but they raised him like his grandchild), real Baek Seoan's mother is also involved in this kidnapping case, and is the provider of the phone and gadgets to the kidnapper, Mr. Park the assistant here is also assigned by the mother only. (He thinks that this baek seaon has killed her sister in their childhood, but the reality is, the kidnapper baek seaon is the one that has killed his sister.