Unnoticed, a cat sneaks into an art museum among the visitors. The cat sleeps all day, and no one pays attention to it. When the museum closes for the day, the cat wakes up and sets out on a nightly journey through the exhibition rooms. The paintings and statues come to life, and the cat and his new friends explore the museum. In the morning an employee opens the main entrance, and two cats exit the museum: the main character and a cat from a famous painting.