"Why Her" follows Soo Jae, a ruthless and competent lawyer who doesn't care about anything except winning and destroys everyone that gets in her way. She did all that to survive in a men's world that don't accept her, that didn't think she was good enough and even so, Soo Jae is betrayed by her mentor and got demoted to being a teacher in a college.
There, she meets Gong Chan, a young man who tries to help in any way possible, what she doesn't know it's that they are connected by the past, when Soo Jae was Gong Chan's lawyer when he was framed for killing his sister. He hides that fact, to keep staying by her side.

The drama's premise reminded me of "I Hear Your Voice", specially because of the relation of the main characters and how they're connected with a death. Actually there's a scene that to me it's almost the same: when Gong Chan say that he's waiting to find someone and that person is Soo Jae.
The problem is that Hwang In Youp just didn't work as a main lead. Maybe it was because of his inexperience, but he couldn't get in the same level as Seo Hyun Jin and this weakened the story and also there was no chemistry at all between them.

One good thing about the drama is Seo Hyun Jin's character Soo Jae, she's a badass woman and if the writers had chosen a better actor to be her pair, the drama would definitely be different.