Chicago Med Season 8 Episode 4 revolves around a train accident.

Marcel finds out Blake is leaving town and rushes off to see her, but before he can get there, a subway derails right under his feet. Marcel jumps a police barrier and goes down into the tunnels to try to help. He finds the inventor of the new supertrain, Jack, and the conductor, Nathaniel, both of whom are injured. Jack's injuries are far less severe.

Marcel is determined to do everything he can to save Nathaniel's life. Chicago Fire shows up and Marcel tells them to get him medical supplies. Nathaniel's injuries are so severe he can't wait to be rescued to have surgery; Marcel must do it down here.

Meanwhile, back at Med, the supply chain shortage again affects Will's patient. This time, it's a retired English teacher named Rose who has a severe fungal infection, but the med is perpetually out of stock. Vanessa knows a guy who can get it for her on the black market, but WIll doesn't want to jeopardize his career and his freedom. However, Rose is near death and her husband begs the doctors to do something.

Finally, Charles' therapist ends up in the hospital with a psychosomatic condition, while Asher again tries to prove herself to Archer.

To find out what happens, watch Chicago Med Season 8 Episode 4 online.