On a rainy night in Busan, So-young (Lee ‘IU’ Ji-eun) leaves her baby Woo-sung outside a ‘baby box’, a safe place set up in Korean churches for new mothers to leave unwanted infants.

Instead, he’s picked up by Sang-hyun (Parasite’s Song Kang-ho) who runs an unofficial adoption brokerage and plans to find him a new home.

So-young tracks down both Sang-hyun and his business partner Dong-soo (Gang Dong-won) and decides to join their pursuit (alongside a seven-year-old stowaway from a nearby orphanage), but as they search for Woo-sung’s new family, the unlikely group evolves into something of a family themselves – unaware they’re being tailed by two detectives (Bae Doona, Lee Joo-young) who are determined to stop them.