Romance Is a Bonus Book is about the love story between two people in their 30s, who work in the world of publishing.

Cha Eun Ho is a successful and handsome writer who is also the youngest chief editor at a publishing company. He has a calm demeanor and remains reasonable at work. He then becomes involved in the life of his childhood friend, Kang Dan I who was once a popular copywriter. 

Kang Dan I is now divorced, a single mother, unemployed and struggling in life though still attempts to find a job, but even with her once good career, she cannot. However, in a desperate attempt to find a job, she lies about her background and begins to work as a temporary worker in the same building under none other than Cha Eun Ho. 

As they become involved in each other's life more than often, a love story begins to unfold.