The final episode sees Rumer Willis star as a guest character. She plays a musician on board a train going from Phoenix to Los Angeles.
However, the train crashes and derails, leaving her character in a terrifying life or death situation.
Titled What’s Next, the episode sees the 118 go to save people after the massive train derailment – and decide whether to save her or another victim.
Episode 18 of season 3 airs tonight, May 11, at 8pm on Fox. The show can be watched for free on Sling TV as part of the Happy Hour promotion, which offers free TV between 5pm and midnight each day.