Han Se Gye is a successful actress currently under gossip attacks for running away from an award ceremony. Seo Do Jae is a company director, fighting with shareholders to keep his position. A woman who once a month changes into someone completely else and a man who won't recognise her face anyway. Both of them have secrets that make them afraid of showing their true self, and it is only a question of how will their sudden encounter change their lives.
As far as movie to drama adaptations go, The Beauty Inside is fairly successful.
The show manages to take the main concept (loving someone whose constantly changing) and make it a honest love story. And while there are flaws and drags in the story, as well as some silly decisions, overall the light hearted romantic comedy tone and great chemistry makes for a great, entertaining watch.