Leaning on each other through thick and thin, a trio of best friends stand together as they experience life, love and loss on the brink of turning 40.

Son Ye-jin, Jeon Mi-do, Kim Ji-hyun, Yeon Woo-jin, Lee Moo-saeng, Lee Tae-hwan, An So-hee, Kang Mal-geum, Park Jae-Joon, Park Ji-il, Lee Ji-hyeon, Nam Kee-ae, Song Min-ji, Gi Eun-you, Seo Ji-young, Seo Hyeon-cheol, Cho Won-hee, Lee Kan-hee, Oh Se-young