Summary (taken from Soompi forums):
Magazine reporter Yoon Soo delivers newspapers every dawn to help his older brother, Young Soo, who manages a newspaper branch office.One foggy morning, he noticed Jung Hyo sitting at a park bench and became interested in her.One day, while interviewing a museum curator, he was happy to run (bump) into Jung Hyo accidently, but was disappointed when she did not seem to recognize him.
After running into her at the park several times, he realized that Jung Hyo suffered from sleepwalking. Despite that Yoon Soo's feeling for Jung Hyo is getting deeper...