Seok-woo, a distracted fund manager, barely looks up from his phone as he and his seven-year-old daughter, Soo-an, board the 5:30 AM KTX to Busan. She wants to see her mother. He wants to close a deal. Their relationship is a series of missed connections.

If you are looking for the specific sequel, the proper title is:

They are now past the point the pirated copy ever reached. No script. No spoilers. Just the next car, the next shadow, and the sound of thousands of sprinting feet.