From MangaHelpers:

Katou Chihaya is the daughter of major construction contractor company's president. Just after graduating from high school, she attended a business party with her father and was being pestered by another company president's son so she made him faint with a karate chop. Just when Chihaya was wondering what to do, another company president's son, who calls himself the Prince on the white horse, happened to see everything and became interested in Chihaya. However, Chihaya couldn't be bothered to even tell him her name so their conversation only ended in a promise to name themselves if they ever meet again.

Four years later, Chihaya decides to work in a company that's not her father's to prove her own worth. She disguises herself as a plain girl to avoid needless attention, but she unexpectedly finds the "Prince" is her new colleague! It appears that he hasn't discovered her true identity, but what will happen once he does, now that they get along pretty well as colleagues? [Eru13]