Detective Cho, a cop on the edge, is mourning his mother's recent death while under investigation for graft; on top of that he is suddenly put in charge of a seemingly-impenetrable mystery.

Little Black Dress depicts the friendships, jealousies, hopes and failures of four 24-year-old girls. The girls first met as first year students in college. They seem to be enjoying their 20's, but inside they all have worries.

After her engagement ends, Mi-yeon reluctantly adopts a sick dog named Happy. With help from vet Min-su, she begins to heal and rediscover joy.