The frail third-generation chaebol heir, Lee Ha-neul,

is always accompanied by his flawless butler and bodyguard, Han Se-jin.

At school, at home — even in front of the bathroom door —
Se-jin’s overprotectiveness goes far beyond what’s normal.

But behind that excessive care lies a horrifying truth.

Ha-neul discovers that he is not human,
and it is revealed that Se-jin, too, is far from being just a “butler.”

A watcher and the watched.
A test subject and an enhanced human.
Between lies and truth, their relationship begins to unravel into chaos…