You will think it's about revenge through out episode 1 to 15, until u watch final episode.
It's actually about second chance to make things right.

Yoon Hyun Woo (HW) is a loyal employee of Soonyang Company for years. He was sent overseas to withdraw company tactical fund, but he was betrayed and murdered.

After HW was shot, he woke up as 10 years old Jin Do Joon back in year 87. Jin Do Joon (DJ) is
Soonyang's owner Jin Yang Cheol (YC) youngest grandson.
He remembers everything from his life as HW, in the body of JD. In other word, He was reborn as JD, and he took this chance to take revenge. He managed to be successful using his knowledge about the future, and gradually became his grandfather's favorite. After YC died, JD supposed to take over Soonyang, but a car accident took his life..again.

But then after the car accident, he woke up in the hospital, back to current time as HW and found out that he actually survived from the shot and living as JD was only a coma-dream. However, the dream "showed" him of what really happened to JD and he has given a second chance to make things right for both; himself and JD.

This drama has more plot twist than you expected. It has conspiracy in all aspects, politics, family, business, relationship and others. You just CAN'T TRUST anyone.
Everyone in this played really well, and deserve our gratitude.