The Train: Some Lines Should Never Be Crossed is a suspense thriller revolving around Vishal Dixit (Emraan Hashmi), a middle-class man who lives with his wife, Anjali Dixit (Sayali Bhagat), and his five-year-old daughter in Bangkok. One day, Vishal meets Roma Kapoor (Geeta Basra), an attractive married woman and the two fall for each other and decide to have an affair. They end up in a hotel room where they are attacked by an armed man named Tony (Aseem Merchant). Tony robs them and learns about their extra-marital affair. To avoid being caught Roma and Vishal decide to not report the theft. Later, their lives take a turn when they start getting calls from Tony who demands a huge amount as a cost to keep their secret. Will they get rid of Tony by paying him a huge amount or get exposed in front of everyone?