Cécile Green is a tour guide at the Louvre Museum in Paris. While presenting the famous Mona Lisa painting, Cécile spots a little white cat in the crowd.

Yukinoko is the white cat Cécile saw, living at the Louvre with a small feline colony. Despite the other cats being harsh and cold toward him, Yukinoko believes it is better than being out on the street. Curiously, he has not grown beyond being a kitten, but he possesses a mysterious power—he can hide inside the Louvre's paintings.

Marcel is a man who has been a nighttime security guard at the Louvre his whole life. As children, Marcel and his sister would play at the museum; during their visits, she would tell him she could hear the voices of the paintings. But shortly after, his sister disappeared in a cloud of mystery and Marcel has been searching for her ever since.

Soon, these three lives are destined to collide in a way none of them would have ever imagined.