Mi-ho goes to see Hye-jung to find out what the key is for. But Hye-jung is hostile to Mi-ho. After pressing Hye-jung, Mi-ho finds out the shocking truth about her mother and Yu-jin's father, and feels even guiltier towards Yu-jin. Meanwhile, Do-jun finds out that Mi-ho met Hye-jung and contacts ‘...’ on his phone. Finally, Mi-ho finds out that the key is for the resident locker in the apartment.
